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FOUS30 KWBC 021523
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1122 AM EDT Tue Nov 02 2021

Day 1
Valid 16Z Tue Nov 02 2021 - 12Z Wed Nov 03 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

16z update:
No signficant changes were required for excessive categories after
reviewing 12z CAMS/HREF and early global guidance.

Gallina

...South Florida...
Some moisture return from the Atlantic along with slowly
increasing MU CAPE is expected to move ashore
Miami-Dade/Broward/Palm Beach counties.

Precipitable water values, on the heels of weak low-level return
flow from the warm Gulf Stream, are expected to creep up to ~1.5",
and some effective bulk shear of 25 kts lurks nearby across the
southeast Gulf of Mexico, which has trended slightly upward
lately, induced by a shortwave edging eastward through the FL
Panhandle. The Gold Coast has seen 150-300% of their usual two
week precipitation, so the Dry Season has not been as dry as usual
in late October. While local amounts of 3"+ falling at 1.5"+ an
hour rates is non-zero near the coasts of Miami-Dade, Broward, and
Palm Beach counties, it does not appear high enough due to
differing model ideas across the area for a Marginal Risk at this
time.

...Texas...
Convection is firing up across the South Plains in proximity to a
surface low and associated front stretching from the Southern
Plains to the Gulf Coast. With moisture convergence expected to
persist over central Texas and CAPE values approaching 1000J/kg
during the afternoon/evening, this environment may be conducive
for hourly rainfall rates up to 0.50 inch/year. There may be very
isolated that may get over 2 inches of rain, but in general, most
locations will likely remain less than 1.5 inches. The better forcing/instability looks to hold off until day 2.


Campbell/Roth


Day 2
Valid 12Z Wed Nov 03 2021 - 12Z Thu Nov 04 2021

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL OVER PORTIONS
OF TEXAS...

Shortwave energy moving across the Southern/Central Rockies will
eject out into the Plains during this period, pushing the surface
front and the precipitation footprint south. CAPE values of
500-1200 J/Kg will be present across much of the southern half of
the state; which will aid in developing/maintaining scattered to
widespread convection. It will also help support hourly rainfall
rates of 0.50 to 1.50+ inch/hour. Although there is still some
spread with the placement of the QPF maximums, 1 to 3 inches are
expected from South Texas to the Texas/Louisiana border. The
latest WPC QPF trended to having more QPF over South Texas and
central portions of the state, which was a westward trend. The
Marginal Risk area for excessive rainfall was expanded to reflect
this change. These amounts may lead to local flash flooding.

Campbell

Day 3
Valid 12Z Thu Nov 04 2021 - 12Z Fri Nov 05 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Campbell


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!staMWrsF4CoG7aRDUrLCuMj2m5TDk8sqDxcs7Cni49xa= q-KriWxD0bLWxBGKQBq1KjrX0kzJ$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!staMWrsF4CoG7aRDUrLCuMj2m5TDk8sqDxcs7Cni49xa= q-KriWxD0bLWxBGKQBq1KlNJYpS9$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!staMWrsF4CoG7aRDUrLCuMj2m5TDk8sqDxcs7Cni49xa= q-KriWxD0bLWxBGKQBq1KqMWSuQH$=20


$$




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FOUS30 KWBC 021931
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
330 PM EDT Tue Nov 02 2021

Day 1
Valid 16Z Tue Nov 02 2021 - 12Z Wed Nov 03 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

16z update:
No signficant changes were required for excessive categories after
reviewing 12z CAMS/HREF and early global guidance.

Gallina

...South Florida...
Some moisture return from the Atlantic along with slowly
increasing MU CAPE is expected to move ashore
Miami-Dade/Broward/Palm Beach counties.

Precipitable water values, on the heels of weak low-level return
flow from the warm Gulf Stream, are expected to creep up to ~1.5",
and some effective bulk shear of 25 kts lurks nearby across the
southeast Gulf of Mexico, which has trended slightly upward
lately, induced by a shortwave edging eastward through the FL
Panhandle. The Gold Coast has seen 150-300% of their usual two
week precipitation, so the Dry Season has not been as dry as usual
in late October. While local amounts of 3"+ falling at 1.5"+ an
hour rates is non-zero near the coasts of Miami-Dade, Broward, and
Palm Beach counties, it does not appear high enough due to
differing model ideas across the area for a Marginal Risk at this
time.

...Texas...
Convection is firing up across the South Plains in proximity to a
surface low and associated front stretching from the Southern
Plains to the Gulf Coast. With moisture convergence expected to
persist over central Texas and CAPE values approaching 1000J/kg
during the afternoon/evening, this environment may be conducive
for hourly rainfall rates up to 0.50 inch/year. There may be very
isolated that may get over 2 inches of rain, but in general, most
locations will likely remain less than 1.5 inches. The better forcing/instability looks to hold off until day 2.


Campbell/Roth


Day 2
Valid 12Z Wed Nov 03 2021 - 12Z Thu Nov 04 2021

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL OVER PORTIONS
OF TEXAS...

20z update:
...Texas...
12z guidance continues to trend slightly faster initially with the
southward push of the cold front across north-central Texas,
reducing the potential for overlapping surface based convection
and deeper mid-level ascent northward of the boundary. The HREF
probabilities and QPF totals have seen a noted decrease in
probability and coverage of hourly rates over 1" through the
morning/early afternoon hours and so the Marginal Risk has been
trimmed slightly southward. However, return moisture off the
western Gulf will increase instability through the afternoon
increasing the potential for surface based convection by early
evening, both across eastern TX as well across south Texas into
the Rio Grande Valley. The front will slow slightly and with
increased convergence will likely enhance thunderstorm risk.=20
Rates of 1.5-2"/hr increase across the Texas Hill Country toward
Houston Metro by late evening enough to maintain a Marginal Risk,
particularly given soils are a bit more saturated recently per
AHPS anomalies.

Into the evening and overnight hours, Hi-Res CAMs further expand
thunderstorm development across South-Central to southern Texas
with greatest probabilities near Corpus Christi though, areas
further west across the Brush country of South Texas will have
isolated potential of rates in excess of 2"/hr and isolated totals
up to 4" suggesting further expansion of the Marginal Risk area
toward the south even with higher FFG/drier ground conditions.

Gallina


...Texas...
Shortwave energy moving across the Southern/Central Rockies will
eject out into the Plains during this period, pushing the surface
front and the precipitation footprint south. CAPE values of
500-1200 J/Kg will be present across much of the southern half of
the state; which will aid in developing/maintaining scattered to
widespread convection. It will also help support hourly rainfall
rates of 0.50 to 1.50+ inch/hour. Although there is still some
spread with the placement of the QPF maximums, 1 to 3 inches are
expected from South Texas to the Texas/Louisiana border. The
latest WPC QPF trended to having more QPF over South Texas and
central portions of the state, which was a westward trend. The
Marginal Risk area for excessive rainfall was expanded to reflect
this change. These amounts may lead to local flash flooding.

Campbell

Day 3

The Day 3 outlook will be updated by 2030Z.


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!ufyw0UQxmQXnITsJfqS0Ge9mCRaXgFDRSYNlMJ9RBk75= 44bdD52avruNPfE4cTvjOP1cUIEs$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!ufyw0UQxmQXnITsJfqS0Ge9mCRaXgFDRSYNlMJ9RBk75= 44bdD52avruNPfE4cTvjON9vM3hU$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!ufyw0UQxmQXnITsJfqS0Ge9mCRaXgFDRSYNlMJ9RBk75= 44bdD52avruNPfE4cTvjOIZC5DpP$=20


$$




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FOUS30 KWBC 021931
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
331 PM EDT Tue Nov 02 2021

Day 1
Valid 16Z Tue Nov 02 2021 - 12Z Wed Nov 03 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

16z update:
No signficant changes were required for excessive categories after
reviewing 12z CAMS/HREF and early global guidance.

Gallina

...South Florida...
Some moisture return from the Atlantic along with slowly
increasing MU CAPE is expected to move ashore
Miami-Dade/Broward/Palm Beach counties.

Precipitable water values, on the heels of weak low-level return
flow from the warm Gulf Stream, are expected to creep up to ~1.5",
and some effective bulk shear of 25 kts lurks nearby across the
southeast Gulf of Mexico, which has trended slightly upward
lately, induced by a shortwave edging eastward through the FL
Panhandle. The Gold Coast has seen 150-300% of their usual two
week precipitation, so the Dry Season has not been as dry as usual
in late October. While local amounts of 3"+ falling at 1.5"+ an
hour rates is non-zero near the coasts of Miami-Dade, Broward, and
Palm Beach counties, it does not appear high enough due to
differing model ideas across the area for a Marginal Risk at this
time.

...Texas...
Convection is firing up across the South Plains in proximity to a
surface low and associated front stretching from the Southern
Plains to the Gulf Coast. With moisture convergence expected to
persist over central Texas and CAPE values approaching 1000J/kg
during the afternoon/evening, this environment may be conducive
for hourly rainfall rates up to 0.50 inch/year. There may be very
isolated that may get over 2 inches of rain, but in general, most
locations will likely remain less than 1.5 inches. The better forcing/instability looks to hold off until day 2.


Campbell/Roth


Day 2
Valid 12Z Wed Nov 03 2021 - 12Z Thu Nov 04 2021

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL OVER PORTIONS
OF TEXAS...

20z update:
...Texas...
12z guidance continues to trend slightly faster initially with the
southward push of the cold front across north-central Texas,
reducing the potential for overlapping surface based convection
and deeper mid-level ascent northward of the boundary. The HREF
probabilities and QPF totals have seen a noted decrease in
probability and coverage of hourly rates over 1" through the
morning/early afternoon hours and so the Marginal Risk has been
trimmed slightly southward. However, return moisture off the
western Gulf will increase instability through the afternoon
increasing the potential for surface based convection by early
evening, both across eastern TX as well across south Texas into
the Rio Grande Valley. The front will slow slightly and with
increased convergence will likely enhance thunderstorm risk.=20
Rates of 1.5-2"/hr increase across the Texas Hill Country toward
Houston Metro by late evening enough to maintain a Marginal Risk,
particularly given soils are a bit more saturated recently per
AHPS anomalies.

Into the evening and overnight hours, Hi-Res CAMs further expand
thunderstorm development across South-Central to southern Texas
with greatest probabilities near Corpus Christi though, areas
further west across the Brush country of South Texas will have
isolated potential of rates in excess of 2"/hr and isolated totals
up to 4" suggesting further expansion of the Marginal Risk area
toward the south even with higher FFG/drier ground conditions.

Gallina


...Texas...
Shortwave energy moving across the Southern/Central Rockies will
eject out into the Plains during this period, pushing the surface
front and the precipitation footprint south. CAPE values of
500-1200 J/Kg will be present across much of the southern half of
the state; which will aid in developing/maintaining scattered to
widespread convection. It will also help support hourly rainfall
rates of 0.50 to 1.50+ inch/hour. Although there is still some
spread with the placement of the QPF maximums, 1 to 3 inches are
expected from South Texas to the Texas/Louisiana border. The
latest WPC QPF trended to having more QPF over South Texas and
central portions of the state, which was a westward trend. The
Marginal Risk area for excessive rainfall was expanded to reflect
this change. These amounts may lead to local flash flooding.

Campbell

Day 3
Valid 12Z Thu Nov 04 2021 - 12Z Fri Nov 05 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Gallina


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!qj6rJPEImw6ItoNMVff949sOSZAtBzA_6P8pA_sHn0Pl= U2JizWeK5uIMwa7MpZ2ICHmk1UKV$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!qj6rJPEImw6ItoNMVff949sOSZAtBzA_6P8pA_sHn0Pl= U2JizWeK5uIMwa7MpZ2ICPDu1cFM$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!qj6rJPEImw6ItoNMVff949sOSZAtBzA_6P8pA_sHn0Pl= U2JizWeK5uIMwa7MpZ2ICMXvGJXD$=20


$$




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FOUS30 KWBC 121531
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1030 AM EST Fri Nov 12 2021

Day 1
Valid 16Z Fri Nov 12 2021 - 12Z Sat Nov 13 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE NORTHWEST AND NORTHEAST...

16z update: Across the Northwest no substantive changes were made
to the Marginal Risk area provided trends in remote sensing and
observational data, as well as newer 12z Hi-Res CAM guidance and
HREF probabilities remain on track for placement and forecast
reasoning.

For the Northeast, small adjustments to the western boundary were
made based on RADAR trends and recent Mesoscale Precipitation
Discussion 1127 issued at 1445z. IVT values remain in the 1000
kg/m/s^2 range which is the 99th percentile for this time of year,
given ample confluent moisture streams and PWs of 1-1.3" (95th
percentile) for New England.=20=20

Gallina

...Northwest...
The atmospheric river event from Thu-Thu night will start to wind
down this morning, with lingering impacts expected across portions
of the Coastal Range and Cascades. As is typically the case,
strong convergence zones will likely develop despite much of the
energy starting to translate east, out of the region. This could
lead to periods of heavy rain through Friday afternoon. For this
reason, hourly rain rates could still be as high as 0.50-0.75
inches through the first half of the forecast period with areal
average precipitation totals of 1-2+ inches within 12 hours. As a
result, flooding issues may continue, especially across the steep
terrain and any burn scar areas in the Cascades over southwest WA
and northwest OR. Therefore, a Marginal Risk area continues over
these areas.

Farther east today, the main deep-layer WAA/moisture surge
(positive PW and 850-700 moisture flux anomaly) along the upper
level jet axis will shift eastward into across the northern Great
Basin and into the western slopes of the northern Rockies. PW
values of 0.75-1.00" are around 3 standard deviations above normal
per the GEFS/SREF, as is the 850-700 mb moisture flux anomalies
with the uptick in SW-WSW flow. The lack of instability will
likely cap hourly rainfall rates under 0.50". However, 3-hourly
rates between 0.75-1.0" in spots may cause localized runoff issues
given the current FFG, especially over isolated burn scar areas.

...Northeast...
As the main low pressure area continues to deepen/occlude over the
Upper Midwest-Great Lakes, a secondary low will develop along the
main baroclinic zone (triple point) and track across NY and New
England. Robust southerly low-level inflow (50-60kts at 850 mb or
~5 standard deviations above normal per the GEFS/SREF) will allow
for a precipitous increase in moisture flux today ahead of the
cold front, with PWs peaking around 1.25-1.40". The lack of
deep-layer instability (MUCAPEs 100-250 J/kg) will limit the
short-term rainfall rates over this region as well. However, with
the bulk of the rain expected to fall in less than 6 hours, spotty
areas of 1.5-2.0" within 3 hours per the high-res CAMs may lead to
isolated runoff issues given the latest FFG -- especially along
Downeast ME given the heavy rainfall over a week ago (where 14 day
rainfall averages between 150-200% of normal).

Hurley


Day 2
Valid 12Z Sat Nov 13 2021 - 12Z Sun Nov 14 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley

Day 3
Valid 12Z Sun Nov 14 2021 - 12Z Mon Nov 15 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
OLYMPIC PENINSULA AND NORTHERN WASHINGTON CASCADES...

A shortwave trough over the Gulf of Alaska early on Sunday will
pivot eastward and reach the Pacific NW coast on Monday. During
the intervening period, an initial surge of deep-layer
WAA/isentropic ascent and moisture transport ahead of the warm
front will push into western WA-OR Saturday night. The main
Atmospheric River meanwhile will be directed into Vancouver Island
by the start of Day 3 (12Z Sunday), then slowly drop southward
across the Olympic Peninsula and northern WA Cascades Sun-Sun
night ahead of the shortwave trough and associated surface cold
front. Per the CW3E AR Scale, the GEFS and ECWMF are both
indicating a moderate to strong Atmospheric River with a peak
forecast AR rating of 4 on a 5-point scale. Integrated water vapor
transport or IVT values peak between 750-800 kg/m/s during day 3,
with PW values topping out aoa 1.25" along the coast. Per the 00Z
GEFS...SW-WSW flow of 45-55+ kts within the 850-700 mb layer will
lead to moisture flux anomalies of 3-3.5 standard deviations above
normal. As with the departing AR, deep-layer instability will be
scant -- generally 100-250 J/kg tops. However, considering the
aforementioned factors along with the strong upslope component,
pockets with with 1hr (3hr) rainfall rates of at least 0.50"
(1.00") are anticipated, with 24hr total rainfall between
2.5-5.0". Considering the current soil moisture and streamflow
trends per the latest FLASH and SPoRT analyses, this next AR
Sun-sun night could certainly cause additional short-term runoff
issues.

Hurley



Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!seGD1gtPBdx9wyLaXSq__fcXzhzT2dJUhTqoZbWGfPZu= K5d02R0n9kcSCyW2W4YR1hQY7r2W$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!seGD1gtPBdx9wyLaXSq__fcXzhzT2dJUhTqoZbWGfPZu= K5d02R0n9kcSCyW2W4YR1v7qzhaT$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!seGD1gtPBdx9wyLaXSq__fcXzhzT2dJUhTqoZbWGfPZu= K5d02R0n9kcSCyW2W4YR1tOBzEAj$=20


$$




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FOUS30 KWBC 121941
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
240 PM EST Fri Nov 12 2021

Day 1
Valid 16Z Fri Nov 12 2021 - 12Z Sat Nov 13 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE NORTHWEST AND NORTHEAST...

16z update: Across the Northwest no substantive changes were made
to the Marginal Risk area provided trends in remote sensing and
observational data, as well as newer 12z Hi-Res CAM guidance and
HREF probabilities remain on track for placement and forecast
reasoning.

For the Northeast, small adjustments to the western boundary were
made based on RADAR trends and recent Mesoscale Precipitation
Discussion 1127 issued at 1445z. IVT values remain in the 1000
kg/m/s^2 range which is the 99th percentile for this time of year,
given ample confluent moisture streams and PWs of 1-1.3" (95th
percentile) for New England.=20=20

Gallina

...Northwest...
The atmospheric river event from Thu-Thu night will start to wind
down this morning, with lingering impacts expected across portions
of the Coastal Range and Cascades. As is typically the case,
strong convergence zones will likely develop despite much of the
energy starting to translate east, out of the region. This could
lead to periods of heavy rain through Friday afternoon. For this
reason, hourly rain rates could still be as high as 0.50-0.75
inches through the first half of the forecast period with areal
average precipitation totals of 1-2+ inches within 12 hours. As a
result, flooding issues may continue, especially across the steep
terrain and any burn scar areas in the Cascades over southwest WA
and northwest OR. Therefore, a Marginal Risk area continues over
these areas.

Farther east today, the main deep-layer WAA/moisture surge
(positive PW and 850-700 moisture flux anomaly) along the upper
level jet axis will shift eastward into across the northern Great
Basin and into the western slopes of the northern Rockies. PW
values of 0.75-1.00" are around 3 standard deviations above normal
per the GEFS/SREF, as is the 850-700 mb moisture flux anomalies
with the uptick in SW-WSW flow. The lack of instability will
likely cap hourly rainfall rates under 0.50". However, 3-hourly
rates between 0.75-1.0" in spots may cause localized runoff issues
given the current FFG, especially over isolated burn scar areas.

...Northeast...
As the main low pressure area continues to deepen/occlude over the
Upper Midwest-Great Lakes, a secondary low will develop along the
main baroclinic zone (triple point) and track across NY and New
England. Robust southerly low-level inflow (50-60kts at 850 mb or
~5 standard deviations above normal per the GEFS/SREF) will allow
for a precipitous increase in moisture flux today ahead of the
cold front, with PWs peaking around 1.25-1.40". The lack of
deep-layer instability (MUCAPEs 100-250 J/kg) will limit the
short-term rainfall rates over this region as well. However, with
the bulk of the rain expected to fall in less than 6 hours, spotty
areas of 1.5-2.0" within 3 hours per the high-res CAMs may lead to
isolated runoff issues given the latest FFG -- especially along
Downeast ME given the heavy rainfall over a week ago (where 14 day
rainfall averages between 150-200% of normal).

Hurley


Day 2
Valid 12Z Sat Nov 13 2021 - 12Z Sun Nov 14 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
OLYMPIC PENINSULA AND NORTHERN WASHINGTON CASCADES...

A broad area of subtropical moisture and warming will in place
across the northeast Pacific Ocean, a subtle shortwave emerging
from the sub-tropics will amplify along a tightening height
gradient along the southeast periphery of the larger scale Gulf of
Alaska closed low. This wave will quickly amplify, corral the
enhance moisture and strengthen/tighten a warm front that extends
eastward toward the Pacific Northwest. Total PWats of 1.25-1.6"
will pool along the front with 65-70kt southwesterly jet enhancing
the strong WAA along and ahead of the boundary into the Olympic
Peninsula toward 00-03z Sunday. This WAA and ample moisture is
about 2.25-2.75 Standard Anomalies or 99th percentiles, combined
with strength of flux (60-70kts) in the 850-7H layer, supports IVT
values in excess of 800 kg/m/s . Limiting factor is going to be
duration of this event, as the warm front and associated WAA peaks
about 06z but reduces quickly toward 12z even into the northern
Cascades. With that stated, 12z Hi-Res CAMs particularly the ARW
solutions, suggest hourly rates in excess of .5"/hr and 1.5-3"
totals by 12z. Given 0-40cm soil saturation values are nearly
100% per NASA SPoRT LIS anomaly products this should result in
nearly all rainfall running off increasing rapid onset flooding
risk. Freezing levels will initially be at or just below the
higher peaks level (mainly in the Cascades), the strength of the
WAA, coupled with rainfall could also quickly convert any of the
snow to runoff as well. As such and in coordination with local
forecast office in Seattle, a Marginal Risk of Excessive Rainfall
has been introduced for the day 2 period, but particularly after
14.00z Saturday evening into Sunday morning for the Olympic Range
and Northern Cascade range of Washington.

Gallina

Day 3

The Day 3 outlook will be updated by 2030Z.


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!pObybZOCHYz3qVCOFvLLgFEpD5t__2rz-5-3FEDmc7C7= -R8CBRnXdZ0qP8jQm-yzORXgn73x$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!pObybZOCHYz3qVCOFvLLgFEpD5t__2rz-5-3FEDmc7C7= -R8CBRnXdZ0qP8jQm-yzOUvQrBBM$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!pObybZOCHYz3qVCOFvLLgFEpD5t__2rz-5-3FEDmc7C7= -R8CBRnXdZ0qP8jQm-yzOSdzjy7a$=20


$$




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FOUS30 KWBC 121941
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
240 PM EST Fri Nov 12 2021

Day 1
Valid 16Z Fri Nov 12 2021 - 12Z Sat Nov 13 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE NORTHWEST AND NORTHEAST...

16z update: Across the Northwest no substantive changes were made
to the Marginal Risk area provided trends in remote sensing and
observational data, as well as newer 12z Hi-Res CAM guidance and
HREF probabilities remain on track for placement and forecast
reasoning.

For the Northeast, small adjustments to the western boundary were
made based on RADAR trends and recent Mesoscale Precipitation
Discussion 1127 issued at 1445z. IVT values remain in the 1000
kg/m/s^2 range which is the 99th percentile for this time of year,
given ample confluent moisture streams and PWs of 1-1.3" (95th
percentile) for New England.=20=20

Gallina

...Northwest...
The atmospheric river event from Thu-Thu night will start to wind
down this morning, with lingering impacts expected across portions
of the Coastal Range and Cascades. As is typically the case,
strong convergence zones will likely develop despite much of the
energy starting to translate east, out of the region. This could
lead to periods of heavy rain through Friday afternoon. For this
reason, hourly rain rates could still be as high as 0.50-0.75
inches through the first half of the forecast period with areal
average precipitation totals of 1-2+ inches within 12 hours. As a
result, flooding issues may continue, especially across the steep
terrain and any burn scar areas in the Cascades over southwest WA
and northwest OR. Therefore, a Marginal Risk area continues over
these areas.

Farther east today, the main deep-layer WAA/moisture surge
(positive PW and 850-700 moisture flux anomaly) along the upper
level jet axis will shift eastward into across the northern Great
Basin and into the western slopes of the northern Rockies. PW
values of 0.75-1.00" are around 3 standard deviations above normal
per the GEFS/SREF, as is the 850-700 mb moisture flux anomalies
with the uptick in SW-WSW flow. The lack of instability will
likely cap hourly rainfall rates under 0.50". However, 3-hourly
rates between 0.75-1.0" in spots may cause localized runoff issues
given the current FFG, especially over isolated burn scar areas.

...Northeast...
As the main low pressure area continues to deepen/occlude over the
Upper Midwest-Great Lakes, a secondary low will develop along the
main baroclinic zone (triple point) and track across NY and New
England. Robust southerly low-level inflow (50-60kts at 850 mb or
~5 standard deviations above normal per the GEFS/SREF) will allow
for a precipitous increase in moisture flux today ahead of the
cold front, with PWs peaking around 1.25-1.40". The lack of
deep-layer instability (MUCAPEs 100-250 J/kg) will limit the
short-term rainfall rates over this region as well. However, with
the bulk of the rain expected to fall in less than 6 hours, spotty
areas of 1.5-2.0" within 3 hours per the high-res CAMs may lead to
isolated runoff issues given the latest FFG -- especially along
Downeast ME given the heavy rainfall over a week ago (where 14 day
rainfall averages between 150-200% of normal).

Hurley


Day 2
Valid 12Z Sat Nov 13 2021 - 12Z Sun Nov 14 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
OLYMPIC PENINSULA AND NORTHERN WASHINGTON CASCADES...

A broad area of subtropical moisture and warming will in place
across the northeast Pacific Ocean, a subtle shortwave emerging
from the sub-tropics will amplify along a tightening height
gradient along the southeast periphery of the larger scale Gulf of
Alaska closed low. This wave will quickly amplify, corral the
enhance moisture and strengthen/tighten a warm front that extends
eastward toward the Pacific Northwest. Total PWats of 1.25-1.6"
will pool along the front with 65-70kt southwesterly jet enhancing
the strong WAA along and ahead of the boundary into the Olympic
Peninsula toward 00-03z Sunday. This WAA and ample moisture is
about 2.25-2.75 Standard Anomalies or 99th percentiles, combined
with strength of flux (60-70kts) in the 850-7H layer, supports IVT
values in excess of 800 kg/m/s . Limiting factor is going to be
duration of this event, as the warm front and associated WAA peaks
about 06z but reduces quickly toward 12z even into the northern
Cascades. With that stated, 12z Hi-Res CAMs particularly the ARW
solutions, suggest hourly rates in excess of .5"/hr and 1.5-3"
totals by 12z. Given 0-40cm soil saturation values are nearly
100% per NASA SPoRT LIS anomaly products this should result in
nearly all rainfall running off increasing rapid onset flooding
risk. Freezing levels will initially be at or just below the
higher peaks level (mainly in the Cascades), the strength of the
WAA, coupled with rainfall could also quickly convert any of the
snow to runoff as well. As such and in coordination with local
forecast office in Seattle, a Marginal Risk of Excessive Rainfall
has been introduced for the day 2 period, but particularly after
14.00z Saturday evening into Sunday morning for the Olympic Range
and Northern Cascade range of Washington.

Gallina

Day 3
Valid 12Z Sun Nov 14 2021 - 12Z Mon Nov 15 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE OLYMPIC
PENINSULA AND NORTHERN WASHINGTON CASCADES...

After the initial moisture surge with the warm front early Sunday
morning, there may be some residual enhanced convergence lingering
through the northern Washington Cascades at the start of the Day 3
forecast time period (14.12z). Synopically, the leading shortwave
will remain focused making landfall into central BC by early
morning Sunday, while the upstream larger scale closed low
descends in latitude toward the southeast. As such the
subtropical moisture plume will once again narrow and focus north
of the U.S. boarder into Vancouver Island. Southwesterly onshore
flow at 25-30kts will keep modest ascent and moisture convergence
for lighter showers across the Olympic Peninsula into the Northern
Cascades with freezing levels rising above all but the most
extreme peaks.=20

There has been some uncertainty to the timing of the shortwave and
therefore the placement and southward push of the frontal zone by
early afternoon into overnight hours. Current trends suggest
increasing confidence toward the boundary sliding south into
western Washington before stalling ahead of the further upstream
larger scale height-falls. Solid moisture convergence along the
frontal zone accompanied by 1-1.25" Total PWat Values support a
longer duration moderate to heavy rainfall event to start
unfolding throughout the day, strengthening with lower level flow
and increased moisture to 1.25-1.4" by overnight to 15.12z on
Monday. The 12z GFS/ECMWF/CMC solutions suggest similar
orientation and placement of the frontal zone across the Olympic
Range and across into the northern Washington Cascades with 24hr
totals of 4-7" and 3-6",respectively. Unlike on Day 2, the
overall strength of flow (30-40kts at 85H) and depth of moisture
support generally a magnitude lower in intensity given IVT values
in the 300 to 400 range perhaps peaking near 600-700 kg/m/s toward
15.12z but it is the length of duration, at 12-18 hour with
nearly stationary or very slow southward progression of the
boundary that is fairly orthogonal to the coastal ranges supports
a increase of category to a Slight Risk of Excessive Rainfall.=20
Colorado State ERO first guess suggests 20-35% probability to
1-2yr ARI exceedance, which appears to correlate well with a high
end Slight Risk area providing further confidence in this upgrade.
=20=20

Gallina



Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!sfddVhbI6eXcfMbFqltpvlG1aizugG-1ecigL8EvBy-c= jhvJLPVhL4MQCCt_GuwCfjge7kAy$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!sfddVhbI6eXcfMbFqltpvlG1aizugG-1ecigL8EvBy-c= jhvJLPVhL4MQCCt_GuwCfk3A5PXQ$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!sfddVhbI6eXcfMbFqltpvlG1aizugG-1ecigL8EvBy-c= jhvJLPVhL4MQCCt_GuwCfiSv5hxc$=20


$$




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FOUS30 KWBC 131533
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1032 AM EST Sat Nov 13 2021

Day 1
Valid 16Z Sat Nov 13 2021 - 12Z Sun Nov 14 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
OLYMPIC PENINSULA AND NORTHERN WASHINGTON CASCADES...

16z Update:
While the 12z RAOB sounding denoted average total PWat values
(.58") at UIL this morning, CIRA Layered Precipitable Water (LPW)
suite shows enhanced moisture supporting forecast values of
1.3-1.6" along and east of the main cold front quickly advancing
with the shortwave feature and developing surface cyclone (near
45N138W). Observational trends along with 12z CAMs suggest some
modest instability is present at/along the warm front and warm
sector with values of 250 J/kg. As such, timing of the frontal
zone and intersection with the Olympic peninsula should see light
showers around 00z before the potential for stronger shallow
updrafts around 03z-04z. HRRR and ARW solutions all support
multiple hours (2-3) of .5"/hr rates along the western slopes,
with occasional maximum rates up to .75"/hr resulting in pockets
of 2-3" totals along the Olympic Range before translating to the
central and northern Washington Cascades. This is a slight uptick
in intensity; however, the short-duration with respect to typical
AR suggests impact will be just below Slight Risk category. As
such, no changes were made to the placement of the Marginal Risk
for Day 1.

Gallina

---Prior Discussion---
With broad area of subtropical moisture and maturing Warm Conveyor
Belt (WCB) in place across the northeast Pacific Ocean, an
elongated, flat mid-level vort lobe emerging from the sub-tropics
will amplify along the southeast periphery of the larger scale
Gulf of Alaska closed low...leading to strengthening mid-upper
level confluence and a tightened N-S upper height gradient. As
this occurs, the bolstered WCB will funnel toward the Pacific
Northwest, along with a sharpening warm front. Total PWs of
1.25-1.5" will pool along the front with a 50-60kt southwesterly
jet enhancing the strong WAA along and ahead of the boundary into
the Olympic Peninsula toward 00-03Z Sunday. 850-700 mb moisture
flux anomalies are between +3 and +4 standard deviations per the
GEFS, while the aforementioned PWs would approach or exceed the
daily record at UIL for mid November per the SPC sounding
climatology page.

The limiting factor is going to be duration of this event, not
starting in earnest until the latter half of the period (after 00Z
Sun), along with the warm front and associated robust deep-layer
WAA/isentropic ascent peaking around 06Z before quickly waning
toward 12Z. With that stated, 00Z high-res CAMs depict hourly
rates in excess of .5"/hr and 1.5-3+" totals by 12Z. Given 0-100cm
soil saturation values are nearly 100% per NASA SPoRT, this should
result in nearly all rainfall running off increasing rapid onset
flooding risk. While freezing levels will initially be at or just
below the higher peaks level (mainly in the Cascades), the
strength of the WAA, coupled with rainfall could also quickly
convert any of the snow to runoff as well. As such, the Marginal
Risk that was added to yesterday's Day 2 ERO will continue into
the Day 1 period, mainly after 00Z Sunday, for the Olympic Range
and Northern Cascade range of Washington.

Hurley


Day 2
Valid 12Z Sun Nov 14 2021 - 12Z Mon Nov 15 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE OLYMPIC
PENINSULA AND NORTHERN WASHINGTON CASCADES...

After the initial moisture surge with the warm front early Sunday
morning, there may be some residual enhanced convergence lingering
through the northern Washington Cascades at the start of the Day 2
forecast time period (12Z 11/14). Synoptically, the leading
shortwave will remain focused making landfall into central BC by
early morning Sunday, while the upstream larger-scale trough
begins to phase with the southern stream wave around 42N/135W
toward the end of the day 2 period (12Z 11/15). As such the
subtropical moisture plume will once again narrow and focus north
of the U.S. boarder into Vancouver Island. Southwesterly 850 mb
onshore flow around 35-50 kts will keep modest ascent and moisture
convergence for lighter showers across the Olympic Peninsula into
the Northern Cascades with freezing levels rising above all but
the most extreme peaks.=20

There had been some uncertainty to the timing of the shortwave and
therefore the placement and southward push of the frontal zone and
pre-frontal Atmospheric River (AR) by early afternoon Sunday into
Sunday night. Recent trends suggest increasing confidence toward
the boundary sliding south into western Washington before stalling
ahead of the further upstream larger scale height-falls. This will
allow the elongated AR to remain directed into western WA and the
northern WA Cascades for several hours, as the initial WSW-ENE
orientation of the AR becomes more SW-NE oriented Sunday night. A
prolonged period of deep-layer moisture transport and orographic
enhancement along the frontal zone, accompanied by 1-1.25" Total
PW Values support a longer duration moderate to heavy rainfall
event Sun-Sun night.

During the entire D2 period (12Z Sun 11/14-12Z Mon 11/15), the
Center for Western Weather and Water Extremes (CW3E) is
forecasting a level 4 AR with integrated water vapor transport or
IVT persisting between 500-750 kg/m/s. The ECMWF, UKMET, and GEM global/regional runs indicate 24hr totals of 3-6+ inches across
the Olympic Peninsula and northern WA Cascades; however, the GFS
is slower with the frontal push and thus a bit farther north with
the max QPF over the Cascades (highest totals across the border
into southern BC). The FV3 is a bit farther south, supportive of
the non-GFS camp, while the NAM CONUS Nest indicates scattered
maxima over 7".

As noted in the previous discussion, given the prolonged duration
of this particular AR event, with nearly stationary or very slow
southward progression of the boundary that is fairly orthogonal to
the coastal ranges, a Slight Risk again appears warranted for the
now Day 2 ERO period. Colorado State ERO first guess suggests
20-35% probability of 1-2yr ARI exceedance, which appears to
correlate well with a high-end Slight Risk.=20=20=20

Hurley/Gallina


Day 3
Valid 12Z Mon Nov 15 2021 - 12Z Tue Nov 16 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE OLYMPIC PENINSULA AND NORTHERN WASHINGTON CASCADES...

The aforementioned phased shortwaves and associated surface cold
front will finally push onshore the Pacific NW coast by Monday
afternoon. Behind the front, a precipitous drop in total PW and
freezing levels will ensue, as the AR weakens and becomes more W-E
oriented while dropping quickly southward into northern CA Monday
night. Until then however (at least through early Monday
afternoon), spotty 1hr rainfall rates ~0.50" with more widespread
3hr rates of aoa 1.00" can still be expected across the Olympic
Peninsula and northern-central WA Cascades. Maximum, additional
areal-average QPF between 12-21Z Mon (prior to the frontal
passage) is expected to range between 1.5 and 3+" per a non-GFS
guidance consensus. The GFS meanwhile is much heavier compared to
the rest of the guidance (more widespread areas of 3-5" over the
Olympics and northern WA Cascades), due to the slower progression
of the upper trough/surface front and pre-frontal AR compared to
the other models. Will include a Marginal Risk in the Day 3 ERO
(12Z Mon-12Z Tue) to bridge the Slight Risk on Day 2 to a much
drier regime by Day 4 (Tue-Tue night).

Hurley




Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!rcctJ4qqJZM2wOF1EloM_YI9BH1yTo85D3pkOSHl8I00= f3Wq9eqky_xDEkYCNHtOCttCo_U3$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!rcctJ4qqJZM2wOF1EloM_YI9BH1yTo85D3pkOSHl8I00= f3Wq9eqky_xDEkYCNHtOClnKjKs4$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!rcctJ4qqJZM2wOF1EloM_YI9BH1yTo85D3pkOSHl8I00= f3Wq9eqky_xDEkYCNHtOCsn30dpq$=20


$$




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FOUS30 KWBC 131944
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
243 PM EST Sat Nov 13 2021

Day 1
Valid 16Z Sat Nov 13 2021 - 12Z Sun Nov 14 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
OLYMPIC PENINSULA AND NORTHERN WASHINGTON CASCADES...

16z Update:
While the 12z RAOB sounding denoted average total PWat values
(.58") at UIL this morning, CIRA Layered Precipitable Water (LPW)
suite shows enhanced moisture supporting forecast values of
1.3-1.6" along and east of the main cold front quickly advancing
with the shortwave feature and developing surface cyclone (near
45N138W). Observational trends along with 12z CAMs suggest some
modest instability is present at/along the warm front and warm
sector with values of 250 J/kg. As such, timing of the frontal
zone and intersection with the Olympic peninsula should see light
showers around 00z before the potential for stronger shallow
updrafts around 03z-04z. HRRR and ARW solutions all support
multiple hours (2-3) of .5"/hr rates along the western slopes,
with occasional maximum rates up to .75"/hr resulting in pockets
of 2-3" totals along the Olympic Range before translating to the
central and northern Washington Cascades. This is a slight uptick
in intensity; however, the short-duration with respect to typical
AR suggests impact will be just below Slight Risk category. As
such, no changes were made to the placement of the Marginal Risk
for Day 1.

Gallina

---Prior Discussion---
With broad area of subtropical moisture and maturing Warm Conveyor
Belt (WCB) in place across the northeast Pacific Ocean, an
elongated, flat mid-level vort lobe emerging from the sub-tropics
will amplify along the southeast periphery of the larger scale
Gulf of Alaska closed low...leading to strengthening mid-upper
level confluence and a tightened N-S upper height gradient. As
this occurs, the bolstered WCB will funnel toward the Pacific
Northwest, along with a sharpening warm front. Total PWs of
1.25-1.5" will pool along the front with a 50-60kt southwesterly
jet enhancing the strong WAA along and ahead of the boundary into
the Olympic Peninsula toward 00-03Z Sunday. 850-700 mb moisture
flux anomalies are between +3 and +4 standard deviations per the
GEFS, while the aforementioned PWs would approach or exceed the
daily record at UIL for mid November per the SPC sounding
climatology page.

The limiting factor is going to be duration of this event, not
starting in earnest until the latter half of the period (after 00Z
Sun), along with the warm front and associated robust deep-layer
WAA/isentropic ascent peaking around 06Z before quickly waning
toward 12Z. With that stated, 00Z high-res CAMs depict hourly
rates in excess of .5"/hr and 1.5-3+" totals by 12Z. Given 0-100cm
soil saturation values are nearly 100% per NASA SPoRT, this should
result in nearly all rainfall running off increasing rapid onset
flooding risk. While freezing levels will initially be at or just
below the higher peaks level (mainly in the Cascades), the
strength of the WAA, coupled with rainfall could also quickly
convert any of the snow to runoff as well. As such, the Marginal
Risk that was added to yesterday's Day 2 ERO will continue into
the Day 1 period, mainly after 00Z Sunday, for the Olympic Range
and Northern Cascade range of Washington.

Hurley


Day 2
Valid 12Z Sun Nov 14 2021 - 12Z Mon Nov 15 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE OLYMPIC
PENINSULA AND NORTHERN WASHINGTON CASCADES...

21z Update:
A notable but not significant shift toward a greater amplification
of the initial shortwave late on Day 1 into early Day 2, denotes a
bit stronger downstream ridging and less orthogonal orientation of
the frontal zone and maximized moisture convergence zone across
Washington into British Columbia. A slight thinning of the AR
moisture plume Sunday afternoon into evening and directed flow
focused greater into Vancouver Island and downstream into the
Southern Canadian Cascade and Rockies has resulted in a overall
reduction in rainfall totals across the region per global
guidance.

The main 5 global members (NAM, GFS, CMC, ECMWF,UKMET) supported
by the their respective ensembles, generally reduced by about 1"
over the 24hr period with totals of 3-5" focused on far NW Olympic
peninsula to northern Washington Cascades, though with greatest
totals now shifted north of the US/Canada boarder. Now that all
12z Hi-Res CAMs forecast period stretches through the entire D2
period, there are overall increased rainfall totals are forecast
based on the higher resolutions, resulting in higher average
totals. The GEM Regional and NAM_Conest depicted typical high
biases with isolated 9-12+" totals seem much to aggressive but the
HRRR and ARW solutions present a more reasonable 4-6+" totals
within the ARWs and HRRR solutions. So this is an odd forecast
period where WPC QPF remained about the same driven by higher fidelity/confidence in higher resolution guidance while the
overall trend was reducing in the global and global ensemble
guidance due to less favorable orientation and placement of the AR
a bit further north. Still, all things considered especially the
saturated grounds and prolonged duration of light to moderate rain
rates, particularly increasing after 15.00z, a high-end Slight
Risk potential is warranted especially exceeding longer-duration
FFG values 6-24hr) further enhancing major to near record river
flooding (per NWC/NWM and NWRFC).

Gallina=20=20


---Prior Discussion---
After the initial moisture surge with the warm front early Sunday
morning, there may be some residual enhanced convergence lingering
through the northern Washington Cascades at the start of the Day 2
forecast time period (12Z 11/14). Synoptically, the leading
shortwave will remain focused making landfall into central BC by
early morning Sunday, while the upstream larger-scale trough
begins to phase with the southern stream wave around 42N/135W
toward the end of the day 2 period (12Z 11/15). As such the
subtropical moisture plume will once again narrow and focus north
of the U.S. boarder into Vancouver Island. Southwesterly 850 mb
onshore flow around 35-50 kts will keep modest ascent and moisture
convergence for lighter showers across the Olympic Peninsula into
the Northern Cascades with freezing levels rising above all but
the most extreme peaks.=20

There had been some uncertainty to the timing of the shortwave and
therefore the placement and southward push of the frontal zone and
pre-frontal Atmospheric River (AR) by early afternoon Sunday into
Sunday night. Recent trends suggest increasing confidence toward
the boundary sliding south into western Washington before stalling
ahead of the further upstream larger scale height-falls. This will
allow the elongated AR to remain directed into western WA and the
northern WA Cascades for several hours, as the initial WSW-ENE
orientation of the AR becomes more SW-NE oriented Sunday night. A
prolonged period of deep-layer moisture transport and orographic
enhancement along the frontal zone, accompanied by 1-1.25" Total
PW Values support a longer duration moderate to heavy rainfall
event Sun-Sun night.

During the entire D2 period (12Z Sun 11/14-12Z Mon 11/15), the
Center for Western Weather and Water Extremes (CW3E) is
forecasting a level 4 AR with integrated water vapor transport or
IVT persisting between 500-750 kg/m/s. The ECMWF, UKMET, and GEM global/regional runs indicate 24hr totals of 3-6+ inches across
the Olympic Peninsula and northern WA Cascades; however, the GFS
is slower with the frontal push and thus a bit farther north with
the max QPF over the Cascades (highest totals across the border
into southern BC). The FV3 is a bit farther south, supportive of
the non-GFS camp, while the NAM CONUS Nest indicates scattered
maxima over 7".

As noted in the previous discussion, given the prolonged duration
of this particular AR event, with nearly stationary or very slow
southward progression of the boundary that is fairly orthogonal to
the coastal ranges, a Slight Risk again appears warranted for the
now Day 2 ERO period. Colorado State ERO first guess suggests
20-35% probability of 1-2yr ARI exceedance, which appears to
correlate well with a high-end Slight Risk.=20=20=20

Hurley


Day 3

The Day 3 outlook will be updated by 2030Z.


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!r2KzF3a54QmD1RvzJFmA8tZ_2YGPZoikRp5a46q5Px2y= cIzuOcO72pW2rGtPtsNt23X8iSOm$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!r2KzF3a54QmD1RvzJFmA8tZ_2YGPZoikRp5a46q5Px2y= cIzuOcO72pW2rGtPtsNt26Oyx5li$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!r2KzF3a54QmD1RvzJFmA8tZ_2YGPZoikRp5a46q5Px2y= cIzuOcO72pW2rGtPtsNt2xPAO33A$=20


$$




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FOUS30 KWBC 131945
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
244 PM EST Sat Nov 13 2021

Day 1
Valid 16Z Sat Nov 13 2021 - 12Z Sun Nov 14 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
OLYMPIC PENINSULA AND NORTHERN WASHINGTON CASCADES...

16z Update:
While the 12z RAOB sounding denoted average total PWat values
(.58") at UIL this morning, CIRA Layered Precipitable Water (LPW)
suite shows enhanced moisture supporting forecast values of
1.3-1.6" along and east of the main cold front quickly advancing
with the shortwave feature and developing surface cyclone (near
45N138W). Observational trends along with 12z CAMs suggest some
modest instability is present at/along the warm front and warm
sector with values of 250 J/kg. As such, timing of the frontal
zone and intersection with the Olympic peninsula should see light
showers around 00z before the potential for stronger shallow
updrafts around 03z-04z. HRRR and ARW solutions all support
multiple hours (2-3) of .5"/hr rates along the western slopes,
with occasional maximum rates up to .75"/hr resulting in pockets
of 2-3" totals along the Olympic Range before translating to the
central and northern Washington Cascades. This is a slight uptick
in intensity; however, the short-duration with respect to typical
AR suggests impact will be just below Slight Risk category. As
such, no changes were made to the placement of the Marginal Risk
for Day 1.

Gallina

---Prior Discussion---
With broad area of subtropical moisture and maturing Warm Conveyor
Belt (WCB) in place across the northeast Pacific Ocean, an
elongated, flat mid-level vort lobe emerging from the sub-tropics
will amplify along the southeast periphery of the larger scale
Gulf of Alaska closed low...leading to strengthening mid-upper
level confluence and a tightened N-S upper height gradient. As
this occurs, the bolstered WCB will funnel toward the Pacific
Northwest, along with a sharpening warm front. Total PWs of
1.25-1.5" will pool along the front with a 50-60kt southwesterly
jet enhancing the strong WAA along and ahead of the boundary into
the Olympic Peninsula toward 00-03Z Sunday. 850-700 mb moisture
flux anomalies are between +3 and +4 standard deviations per the
GEFS, while the aforementioned PWs would approach or exceed the
daily record at UIL for mid November per the SPC sounding
climatology page.

The limiting factor is going to be duration of this event, not
starting in earnest until the latter half of the period (after 00Z
Sun), along with the warm front and associated robust deep-layer
WAA/isentropic ascent peaking around 06Z before quickly waning
toward 12Z. With that stated, 00Z high-res CAMs depict hourly
rates in excess of .5"/hr and 1.5-3+" totals by 12Z. Given 0-100cm
soil saturation values are nearly 100% per NASA SPoRT, this should
result in nearly all rainfall running off increasing rapid onset
flooding risk. While freezing levels will initially be at or just
below the higher peaks level (mainly in the Cascades), the
strength of the WAA, coupled with rainfall could also quickly
convert any of the snow to runoff as well. As such, the Marginal
Risk that was added to yesterday's Day 2 ERO will continue into
the Day 1 period, mainly after 00Z Sunday, for the Olympic Range
and Northern Cascade range of Washington.

Hurley


Day 2
Valid 12Z Sun Nov 14 2021 - 12Z Mon Nov 15 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE OLYMPIC
PENINSULA AND NORTHERN WASHINGTON CASCADES...

21z Update:
A notable but not significant shift toward a greater amplification
of the initial shortwave late on Day 1 into early Day 2, denotes a
bit stronger downstream ridging and less orthogonal orientation of
the frontal zone and maximized moisture convergence zone across
Washington into British Columbia. A slight thinning of the AR
moisture plume Sunday afternoon into evening and directed flow
focused greater into Vancouver Island and downstream into the
Southern Canadian Cascade and Rockies has resulted in a overall
reduction in rainfall totals across the region per global
guidance.

The main 5 global members (NAM, GFS, CMC, ECMWF,UKMET) supported
by the their respective ensembles, generally reduced by about 1"
over the 24hr period with totals of 3-5" focused on far NW Olympic
peninsula to northern Washington Cascades, though with greatest
totals now shifted north of the US/Canada boarder. Now that all
12z Hi-Res CAMs forecast period stretches through the entire D2
period, there are overall increased rainfall totals are forecast
based on the higher resolutions, resulting in higher average
totals. The GEM Regional and NAM_Conest depicted typical high
biases with isolated 9-12+" totals seem much to aggressive but the
HRRR and ARW solutions present a more reasonable 4-6+" totals
within the ARWs and HRRR solutions. So this is an odd forecast
period where WPC QPF remained about the same driven by higher fidelity/confidence in higher resolution guidance while the
overall trend was reducing in the global and global ensemble
guidance due to less favorable orientation and placement of the AR
a bit further north. Still, all things considered especially the
saturated grounds and prolonged duration of light to moderate rain
rates, particularly increasing after 15.00z, a high-end Slight
Risk potential is warranted especially exceeding longer-duration
FFG values 6-24hr) further enhancing major to near record river
flooding (per NWC/NWM and NWRFC).

Gallina=20=20


---Prior Discussion---
After the initial moisture surge with the warm front early Sunday
morning, there may be some residual enhanced convergence lingering
through the northern Washington Cascades at the start of the Day 2
forecast time period (12Z 11/14). Synoptically, the leading
shortwave will remain focused making landfall into central BC by
early morning Sunday, while the upstream larger-scale trough
begins to phase with the southern stream wave around 42N/135W
toward the end of the day 2 period (12Z 11/15). As such the
subtropical moisture plume will once again narrow and focus north
of the U.S. boarder into Vancouver Island. Southwesterly 850 mb
onshore flow around 35-50 kts will keep modest ascent and moisture
convergence for lighter showers across the Olympic Peninsula into
the Northern Cascades with freezing levels rising above all but
the most extreme peaks.=20

There had been some uncertainty to the timing of the shortwave and
therefore the placement and southward push of the frontal zone and
pre-frontal Atmospheric River (AR) by early afternoon Sunday into
Sunday night. Recent trends suggest increasing confidence toward
the boundary sliding south into western Washington before stalling
ahead of the further upstream larger scale height-falls. This will
allow the elongated AR to remain directed into western WA and the
northern WA Cascades for several hours, as the initial WSW-ENE
orientation of the AR becomes more SW-NE oriented Sunday night. A
prolonged period of deep-layer moisture transport and orographic
enhancement along the frontal zone, accompanied by 1-1.25" Total
PW Values support a longer duration moderate to heavy rainfall
event Sun-Sun night.

During the entire D2 period (12Z Sun 11/14-12Z Mon 11/15), the
Center for Western Weather and Water Extremes (CW3E) is
forecasting a level 4 AR with integrated water vapor transport or
IVT persisting between 500-750 kg/m/s. The ECMWF, UKMET, and GEM global/regional runs indicate 24hr totals of 3-6+ inches across
the Olympic Peninsula and northern WA Cascades; however, the GFS
is slower with the frontal push and thus a bit farther north with
the max QPF over the Cascades (highest totals across the border
into southern BC). The FV3 is a bit farther south, supportive of
the non-GFS camp, while the NAM CONUS Nest indicates scattered
maxima over 7".

As noted in the previous discussion, given the prolonged duration
of this particular AR event, with nearly stationary or very slow
southward progression of the boundary that is fairly orthogonal to
the coastal ranges, a Slight Risk again appears warranted for the
now Day 2 ERO period. Colorado State ERO first guess suggests
20-35% probability of 1-2yr ARI exceedance, which appears to
correlate well with a high-end Slight Risk.=20=20=20

Hurley


Day 3
Valid 12Z Mon Nov 15 2021 - 12Z Tue Nov 16 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE OLYMPIC PENINSULA AND NORTHERN WASHINGTON CASCADES...

At the start of the forecast period 15.12z, there is increasing
convergence in global guidance that the AR will be ongoing in
earnest across the Olympic Peninsula and into the northern
Washington Cascades. 850-7H 50-60kts of southwesterly flow
along/southeast of the frontal zone will transport 1-1.25" Total
PWats reducing to .75-1" into the Cascades, resulting in 500-700
kg/m/s IVT values and best potential for excessive rates.

Upstream strong height-falls from the approaching closed low will
strengthen and veer low level flow and quickly press the cold
front southward along the Washington Coast into Oregon and
California AFTER 16.00z. As such, duration of rainfall along with
crashing freezing levels will reduce the threat for flooding
particularly further south across Oregon/California which had
remained dry through the bulk of the AR on days 1 and 2. As
such, maintained the Marginal Risk of Excessive Rainfall to those
locations mostly affected on day 1 and 2 that will see a
additional 1-3", this includes expasion to the Willapa Hills in
southwest Washington per coordination with Portland WFO.=20

Gallina




Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!qu7wc-_3Vz0AbtcM9hu8_ox5_6onOA56lUwqBwDlBbjs= 2zsyAcstIhUgOyZtqvcryI1X1jYD$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!qu7wc-_3Vz0AbtcM9hu8_ox5_6onOA56lUwqBwDlBbjs= 2zsyAcstIhUgOyZtqvcryCA_MNPG$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!qu7wc-_3Vz0AbtcM9hu8_ox5_6onOA56lUwqBwDlBbjs= 2zsyAcstIhUgOyZtqvcryOXqedj4$=20


$$




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FOUS30 KWBC 141545
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1045 AM EST Sun Nov 14 2021

Day 1
Valid 12Z Sun Nov 14 2021 - 12Z Mon Nov 15 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE OLYMPIC
PENINSULA AND NORTHERN WASHINGTON CASCADES...

16z update:
CIRA LPW suite denotes surge of moisture associated with surface
wave near 41N/141W is increasing along the length of the AR plume.
This AR plume appears to be centering very near the NW tip of the
Olympic Peninsula with very little wavering expected throughout
the remainder of the day. This will bring fairly consistent but
slowly increasing TPW values with that surge reaching to about
1.25", though as the wave nears later in the period could reach up
to 1.5 as the enhanced moisture in the lagging 7-5H layer nears
with the surface wave/shortwave near 12z. With increased
winds/moisture, IVT values in the core of the plume will average
about 600 kg/m/s before increasing to 700-800 by the end of the
forecast period. Along with orographic ascent, should provide
consistent .25"/hr along the peaks of the Olympics and northern WA
Cascades (up to .4"/hr in Canadian slopes). Along the edges of the
plume across SW Washington toward Mt. Rainier, lesser moisture and
rates are expected but again will be very consistent.

12z Hi-Res CAMs all generally agree to the timing of the surface
wave and increase in rainfall rates starting about 03z in the late evening/overnight hours. The trend has been for the peak of rain
rates to be a tad later, centering around 12z...transitioning into
Day 2. Rainfall totals will still be greater than 4-6" across the
core of the Olympic and northern WA Cascades, but with a slight
northerly shift, though Hi-Res CAMs suggest localized totals in
excess of 7+" by 12z are possible. As such, very small
adjustments were made to the Slight Risk toward the north. Totals
are reduced across SW Washington terrain into the Southern WA
Cascades, but given saturated ground conditions the Marginal Risk
area continue to be justified.=20=20=20=20=20

Gallina

---Prior Discussion---
After the initial moisture surge with the warm front early this
morning, there may be a brief respite with the coverage of the
more intense rainfall rates across the Olympics and northern
Cascades. Any break however will be short-lived, as the
Atmospheric River (AR) aligns across the Olympic Peninsula and the
northern WA Cascades and persists for a while. Synoptically, after
the leading shortwave makes landfall into central BC by early this
morning, the larger-scale trough upstream will begin to phase with
the southern stream wave around 42N/135W Sunday night. As such,
the subtropical moisture plume will once again narrow and focus
over the Olympic Peninsula northeastward across the northern WA
Cascades Sunday afternoon-Sunday night. Snow levels will remain
quite high -- generally 7500-9000+ feet MSL -- given the strength
and depth of the WAA behind the warm front. Until the Gulf of AK
shortwave pivots and phases with the southern stream wave (by
Monday morning), the WSW-ENE oriented surface front will stall
across far NW WA and bordering Vancouver Island. This will allow
the elongated AR to remain directed into western WA and the
northern WA Cascades for several hours, as the initial WSW-ENE
orientation of the AR becomes more SW-NE oriented toward the end
of the Day 1 period (by 12Z Mon 11/15). A prolonged period of
deep-layer moisture transport and orographic enhancement along the
frontal zone, accompanied by 1-1.25" Total PW Values support a
longer duration moderate to heavy rainfall event -- especially Sun
afternoon and overnight.=20

During the entire D1 period (12Z Sun 11/14-12Z Mon 11/15), the
Center for Western Weather and Water Extremes (CW3E) is
forecasting a level 4 AR per the preferred ECMWF solution, with
integrated water vapor transport or IVT persisting between 500-800
kg/m/s. The global guidance cluster fairly well with the swaths of
3-6+ inches across the Olympic Peninsula and northern WA Cascades.
Meanwhile, the latest HREF mean shows isolated pockets of 7-9"
totals, supported by the WRF ARW members along with the 00/06Z
HRRRs and FV3. The NAM CONUS Nest continues to exhibit a wet bias
(indicating localized 9-12" totals), while the GEM regional
remains quite broad (high areal bias) with the 4-8" totals.

As noted in the previous discussions, given the prolonged duration
of this particular AR event, with nearly stationary or very slow
southward progression of the boundary that is fairly orthogonal to
the coastal ranges, a Slight Risk again appears warranted for the
now Day 1 ERO period.=20

Hurley



Day 2
Valid 12Z Mon Nov 15 2021 - 12Z Tue Nov 16 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE OLYMPIC PENINSULA AND WASHINGTON CASCADES...

At the start of the forecast period (12Z Mon), there is good model
consensus that the AR will be ongoing in earnest across the
Olympic Peninsula and into the northern Washington Cascades. 45-60
kt of 850-700 mb southwesterly flow along/southeast of the frontal
zone will continue to transport 1-1.25" Total PWs into these areas
for the first several hours of the D2 period, maintaining robust
850-700 mb moisture transport and IVT values between 500-700
kg/m/s. As the phased upper trough and surface cold front push
onshore the Pacific NW between 18-21Z Mon, a quick drop in PWs and
freezing levels will ensue, lowering the rainfall rates and
leading to a quick changeover to snow at the higher elevations.

Therefore, the limited duration of the more intense rain rates
early in the period prior to the FROPA and crashing freezing
levels will reduce the threat for flooding, particularly further
south across Oregon/California which up to this point have
remained dry during this most recent AR event. This despite the
presence of weak post-frontal instability (MUCAPEs <400 J/kg) with
the backing winds/increasing CAA aloft Monday afternoon. As such,
maintained the Marginal Risk of Excessive Rainfall across
locations mostly affected by the AR through the current Day 1
period -- areas that are expected to see an additional 1-3" of
rainfall prior to any changeover to snow.

Hurley



Day 3
Valid 12Z Tue Nov 16 2021 - 12Z Wed Nov 17 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!rU13SDTBG2OgFfjgWiIypziOAlPqSuWJH7JTpXOxjamA= JG6_ykUUHJro9jWBahI7C6ULbKj5$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!rU13SDTBG2OgFfjgWiIypziOAlPqSuWJH7JTpXOxjamA= JG6_ykUUHJro9jWBahI7C1aJpJOL$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!rU13SDTBG2OgFfjgWiIypziOAlPqSuWJH7JTpXOxjamA= JG6_ykUUHJro9jWBahI7Cx8MTpEc$=20


$$




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FOUS30 KWBC 141931
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
231 PM EST Sun Nov 14 2021

Day 1
Valid 16Z Sun Nov 14 2021 - 12Z Mon Nov 15 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE OLYMPIC
PENINSULA AND NORTHERN WASHINGTON CASCADES...

16z update:
CIRA LPW suite denotes surge of moisture associated with surface
wave near 41N/141W is increasing along the length of the AR plume.
This AR plume appears to be centering very near the NW tip of the
Olympic Peninsula with very little wavering expected throughout
the remainder of the day. This will bring fairly consistent but
slowly increasing TPW values with that surge reaching to about
1.25", though as the wave nears later in the period could reach up
to 1.5 as the enhanced moisture in the lagging 7-5H layer nears
with the surface wave/shortwave near 12z. With increased
winds/moisture, IVT values in the core of the plume will average
about 600 kg/m/s before increasing to 700-800 by the end of the
forecast period. Along with orographic ascent, should provide
consistent .25"/hr along the peaks of the Olympics and northern WA
Cascades (up to .4"/hr in Canadian slopes). Along the edges of the
plume across SW Washington toward Mt. Rainier, lesser moisture and
rates are expected but again will be very consistent.

12z Hi-Res CAMs all generally agree to the timing of the surface
wave and increase in rainfall rates starting about 03z in the late evening/overnight hours. The trend has been for the peak of rain
rates to be a tad later, centering around 12z...transitioning into
Day 2. Rainfall totals will still be greater than 4-6" across the
core of the Olympic and northern WA Cascades, but with a slight
northerly shift, though Hi-Res CAMs suggest localized totals in
excess of 7+" by 12z are possible. As such, very small
adjustments were made to the Slight Risk toward the north. Totals
are reduced across SW Washington terrain into the Southern WA
Cascades, but given saturated ground conditions the Marginal Risk
area continue to be justified.=20=20=20=20=20

Gallina

---Prior Discussion---
After the initial moisture surge with the warm front early this
morning, there may be a brief respite with the coverage of the
more intense rainfall rates across the Olympics and northern
Cascades. Any break however will be short-lived, as the
Atmospheric River (AR) aligns across the Olympic Peninsula and the
northern WA Cascades and persists for a while. Synoptically, after
the leading shortwave makes landfall into central BC by early this
morning, the larger-scale trough upstream will begin to phase with
the southern stream wave around 42N/135W Sunday night. As such,
the subtropical moisture plume will once again narrow and focus
over the Olympic Peninsula northeastward across the northern WA
Cascades Sunday afternoon-Sunday night. Snow levels will remain
quite high -- generally 7500-9000+ feet MSL -- given the strength
and depth of the WAA behind the warm front. Until the Gulf of AK
shortwave pivots and phases with the southern stream wave (by
Monday morning), the WSW-ENE oriented surface front will stall
across far NW WA and bordering Vancouver Island. This will allow
the elongated AR to remain directed into western WA and the
northern WA Cascades for several hours, as the initial WSW-ENE
orientation of the AR becomes more SW-NE oriented toward the end
of the Day 1 period (by 12Z Mon 11/15). A prolonged period of
deep-layer moisture transport and orographic enhancement along the
frontal zone, accompanied by 1-1.25" Total PW Values support a
longer duration moderate to heavy rainfall event -- especially Sun
afternoon and overnight.=20

During the entire D1 period (12Z Sun 11/14-12Z Mon 11/15), the
Center for Western Weather and Water Extremes (CW3E) is
forecasting a level 4 AR per the preferred ECMWF solution, with
integrated water vapor transport or IVT persisting between 500-800
kg/m/s. The global guidance cluster fairly well with the swaths of
3-6+ inches across the Olympic Peninsula and northern WA Cascades.
Meanwhile, the latest HREF mean shows isolated pockets of 7-9"
totals, supported by the WRF ARW members along with the 00/06Z
HRRRs and FV3. The NAM CONUS Nest continues to exhibit a wet bias
(indicating localized 9-12" totals), while the GEM regional
remains quite broad (high areal bias) with the 4-8" totals.

As noted in the previous discussions, given the prolonged duration
of this particular AR event, with nearly stationary or very slow
southward progression of the boundary that is fairly orthogonal to
the coastal ranges, a Slight Risk again appears warranted for the
now Day 1 ERO period.=20

Hurley



Day 2
Valid 12Z Mon Nov 15 2021 - 12Z Tue Nov 16 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE OLYMPIC PENINSULA AND NORTHERN WASHINGTON CASCADES...

21z update:
Global guidance along with 12z Hi-Res CAM solutions denoted a
slight slowing in the timing of the approaching shortwave and
height-falls. The associated surface wave will have transitioned
ashore into S BC, but the apex of the approaching shortwave will
result in the the cold front pivoting in the vicinity of the
Olympic Range between 12-15z. This will result in a longer
duration of the plume across the Olympic Range and downstream into
the northern Washington and southern Canadian Cascades. Nearly
all Hi-res CAMs forecast rates in range of .5" for a 3-6 hour
period centered on 12-18z time frame, occasionally reaching
.75"/hr. This results in a general 1-2" increase in rainfall
totals for the Day 2 period and 2-4" values by the end of the
event. By 18-21z, height-falls/CAA will press the front quickly
south and eastward across the region and crash freezing levels
effectively ending the AR event for the most affected areas. Now
that the peak rain-rates have shifted to the Day 2 period with
enhanced overall totals, felt it was prudent to increase Excessive
Rainfall category to a Slight Risk, as all rain is already
compounding on saturated grounds in the area. A Marginal Risk
continues southward for portions of southwest Washington into the
central Washington Cascades that had seen rainfall though at lower
totals, so may be affected by the short-duration intense rainfall
rates as the cold front presses through between 18-16.00z.

Gallina

---Prior Discussion---
At the start of the forecast period (12Z Mon), there is good model
consensus that the AR will be ongoing in earnest across the
Olympic Peninsula and into the northern Washington Cascades. 45-60
kt of 850-700 mb southwesterly flow along/southeast of the frontal
zone will continue to transport 1-1.25" Total PWs into these areas
for the first several hours of the D2 period, maintaining robust
850-700 mb moisture transport and IVT values between 500-700
kg/m/s. As the phased upper trough and surface cold front push
onshore the Pacific NW between 18-21Z Mon, a quick drop in PWs and
freezing levels will ensue, lowering the rainfall rates and
leading to a quick changeover to snow at the higher elevations.

Therefore, the limited duration of the more intense rain rates
early in the period prior to the FROPA and crashing freezing
levels will reduce the threat for flooding, particularly further
south across Oregon/California which up to this point have
remained dry during this most recent AR event. This despite the
presence of weak post-frontal instability (MUCAPEs <400 J/kg) with
the backing winds/increasing CAA aloft Monday afternoon. As such,
maintained the Marginal Risk of Excessive Rainfall across
locations mostly affected by the AR through the current Day 1
period -- areas that are expected to see an additional 1-3" of
rainfall prior to any changeover to snow.

Hurley



Day 3

The Day 3 outlook will be updated by 2030Z.


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!t9payblrTka0RQWiKdTVt2IvrP-NY9JMKqemWyljWAoN= -7jdkp9bqIn5A9b-49bMV39mqLTO$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!t9payblrTka0RQWiKdTVt2IvrP-NY9JMKqemWyljWAoN= -7jdkp9bqIn5A9b-49bMV9dJR-yn$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!t9payblrTka0RQWiKdTVt2IvrP-NY9JMKqemWyljWAoN= -7jdkp9bqIn5A9b-49bMV8U86BD6$=20


$$




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FOUS30 KWBC 141932
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
231 PM EST Sun Nov 14 2021

Day 1
Valid 16Z Sun Nov 14 2021 - 12Z Mon Nov 15 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE OLYMPIC
PENINSULA AND NORTHERN WASHINGTON CASCADES...

16z update:
CIRA LPW suite denotes surge of moisture associated with surface
wave near 41N/141W is increasing along the length of the AR plume.
This AR plume appears to be centering very near the NW tip of the
Olympic Peninsula with very little wavering expected throughout
the remainder of the day. This will bring fairly consistent but
slowly increasing TPW values with that surge reaching to about
1.25", though as the wave nears later in the period could reach up
to 1.5 as the enhanced moisture in the lagging 7-5H layer nears
with the surface wave/shortwave near 12z. With increased
winds/moisture, IVT values in the core of the plume will average
about 600 kg/m/s before increasing to 700-800 by the end of the
forecast period. Along with orographic ascent, should provide
consistent .25"/hr along the peaks of the Olympics and northern WA
Cascades (up to .4"/hr in Canadian slopes). Along the edges of the
plume across SW Washington toward Mt. Rainier, lesser moisture and
rates are expected but again will be very consistent.

12z Hi-Res CAMs all generally agree to the timing of the surface
wave and increase in rainfall rates starting about 03z in the late evening/overnight hours. The trend has been for the peak of rain
rates to be a tad later, centering around 12z...transitioning into
Day 2. Rainfall totals will still be greater than 4-6" across the
core of the Olympic and northern WA Cascades, but with a slight
northerly shift, though Hi-Res CAMs suggest localized totals in
excess of 7+" by 12z are possible. As such, very small
adjustments were made to the Slight Risk toward the north. Totals
are reduced across SW Washington terrain into the Southern WA
Cascades, but given saturated ground conditions the Marginal Risk
area continue to be justified.=20=20=20=20=20

Gallina

---Prior Discussion---
After the initial moisture surge with the warm front early this
morning, there may be a brief respite with the coverage of the
more intense rainfall rates across the Olympics and northern
Cascades. Any break however will be short-lived, as the
Atmospheric River (AR) aligns across the Olympic Peninsula and the
northern WA Cascades and persists for a while. Synoptically, after
the leading shortwave makes landfall into central BC by early this
morning, the larger-scale trough upstream will begin to phase with
the southern stream wave around 42N/135W Sunday night. As such,
the subtropical moisture plume will once again narrow and focus
over the Olympic Peninsula northeastward across the northern WA
Cascades Sunday afternoon-Sunday night. Snow levels will remain
quite high -- generally 7500-9000+ feet MSL -- given the strength
and depth of the WAA behind the warm front. Until the Gulf of AK
shortwave pivots and phases with the southern stream wave (by
Monday morning), the WSW-ENE oriented surface front will stall
across far NW WA and bordering Vancouver Island. This will allow
the elongated AR to remain directed into western WA and the
northern WA Cascades for several hours, as the initial WSW-ENE
orientation of the AR becomes more SW-NE oriented toward the end
of the Day 1 period (by 12Z Mon 11/15). A prolonged period of
deep-layer moisture transport and orographic enhancement along the
frontal zone, accompanied by 1-1.25" Total PW Values support a
longer duration moderate to heavy rainfall event -- especially Sun
afternoon and overnight.=20

During the entire D1 period (12Z Sun 11/14-12Z Mon 11/15), the
Center for Western Weather and Water Extremes (CW3E) is
forecasting a level 4 AR per the preferred ECMWF solution, with
integrated water vapor transport or IVT persisting between 500-800
kg/m/s. The global guidance cluster fairly well with the swaths of
3-6+ inches across the Olympic Peninsula and northern WA Cascades.
Meanwhile, the latest HREF mean shows isolated pockets of 7-9"
totals, supported by the WRF ARW members along with the 00/06Z
HRRRs and FV3. The NAM CONUS Nest continues to exhibit a wet bias
(indicating localized 9-12" totals), while the GEM regional
remains quite broad (high areal bias) with the 4-8" totals.

As noted in the previous discussions, given the prolonged duration
of this particular AR event, with nearly stationary or very slow
southward progression of the boundary that is fairly orthogonal to
the coastal ranges, a Slight Risk again appears warranted for the
now Day 1 ERO period.=20

Hurley



Day 2
Valid 12Z Mon Nov 15 2021 - 12Z Tue Nov 16 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE OLYMPIC PENINSULA AND NORTHERN WASHINGTON CASCADES...

21z update:
Global guidance along with 12z Hi-Res CAM solutions denoted a
slight slowing in the timing of the approaching shortwave and
height-falls. The associated surface wave will have transitioned
ashore into S BC, but the apex of the approaching shortwave will
result in the the cold front pivoting in the vicinity of the
Olympic Range between 12-15z. This will result in a longer
duration of the plume across the Olympic Range and downstream into
the northern Washington and southern Canadian Cascades. Nearly
all Hi-res CAMs forecast rates in range of .5" for a 3-6 hour
period centered on 12-18z time frame, occasionally reaching
.75"/hr. This results in a general 1-2" increase in rainfall
totals for the Day 2 period and 2-4" values by the end of the
event. By 18-21z, height-falls/CAA will press the front quickly
south and eastward across the region and crash freezing levels
effectively ending the AR event for the most affected areas. Now
that the peak rain-rates have shifted to the Day 2 period with
enhanced overall totals, felt it was prudent to increase Excessive
Rainfall category to a Slight Risk, as all rain is already
compounding on saturated grounds in the area. A Marginal Risk
continues southward for portions of southwest Washington into the
central Washington Cascades that had seen rainfall though at lower
totals, so may be affected by the short-duration intense rainfall
rates as the cold front presses through between 18-16.00z.

Gallina

---Prior Discussion---
At the start of the forecast period (12Z Mon), there is good model
consensus that the AR will be ongoing in earnest across the
Olympic Peninsula and into the northern Washington Cascades. 45-60
kt of 850-700 mb southwesterly flow along/southeast of the frontal
zone will continue to transport 1-1.25" Total PWs into these areas
for the first several hours of the D2 period, maintaining robust
850-700 mb moisture transport and IVT values between 500-700
kg/m/s. As the phased upper trough and surface cold front push
onshore the Pacific NW between 18-21Z Mon, a quick drop in PWs and
freezing levels will ensue, lowering the rainfall rates and
leading to a quick changeover to snow at the higher elevations.

Therefore, the limited duration of the more intense rain rates
early in the period prior to the FROPA and crashing freezing
levels will reduce the threat for flooding, particularly further
south across Oregon/California which up to this point have
remained dry during this most recent AR event. This despite the
presence of weak post-frontal instability (MUCAPEs <400 J/kg) with
the backing winds/increasing CAA aloft Monday afternoon. As such,
maintained the Marginal Risk of Excessive Rainfall across
locations mostly affected by the AR through the current Day 1
period -- areas that are expected to see an additional 1-3" of
rainfall prior to any changeover to snow.

Hurley



Day 3
Valid 12Z Tue Nov 16 2021 - 12Z Wed Nov 17 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Gallina


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!tqnLYBGuDDFpM9X04y5gbzEfn0gwG08M5myDOjkH9xtU= f-aEaNMI632gVoKtkG5PAgyXsq45$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!tqnLYBGuDDFpM9X04y5gbzEfn0gwG08M5myDOjkH9xtU= f-aEaNMI632gVoKtkG5PAmDD-a2d$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!tqnLYBGuDDFpM9X04y5gbzEfn0gwG08M5myDOjkH9xtU= f-aEaNMI632gVoKtkG5PArIcVmLw$=20


$$




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FOUS30 KWBC 111546
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1045 AM EST Sat Dec 11 2021

Day 1
Valid 12Z Sat Dec 11 2021 - 12Z Sun Dec 12 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WESTERN OREGON AND NORTHWEST CALIFORNIA, AND FROM PARTS OF
SOUTHWEST WEST VIRGINIA/E KENTUCKY/E TENNESSEE INTO N
GEORGIA/ALABAMA...

16z update:
No changes were required given new 12z guidance, and appears to be
on track with initial forecast for the Oregon and northern
California coastal ranges.

Further east, the southwest to northeast oriented line of showers
and thunderstorms continues to march eastward with a general
downward trend in rainfall intensity. This is particularly the
case along the southwest flank in LA/MS as a subtle speed max
lifts northeast and away from the region. Higher FFG values are
less likely to be exceeded, so have trimmed the Marginal to
northern Alabama/northern Georgia where there are still a few
stronger cells and 12z hi-res CAMS suggestive of isolated hourly
totals of 1-1.25" for at least a few more hours. To the north
across the Cumberland Plateau and into SW WV, the cells are
generally weaker but supportive of .75-1" hourly totals as the
lead convective line marches through. Lower FFG values in the
more complex terrain as well as some mid-level lingering
post-frontal showers still have a low end threat for isolated
flash flooding conditions through about 21z as it clears the
western slopes of the Appalachians.=20=20=20=20

Gallina

Prior Discussion
~~~~~~~~~~~~~~~~~~~~
...Western Oregon and Northwest California...
Atmospheric River event will progress southward along the
Oregon/northern California coast today in advance of a cold front
with precipitable water values around +1 to +1.5 sigma. Right
entrance region of a 130-150kt upper jet will provide large-scale
ascent that will be only somewhat enhanced on upslope flow into
SSW-facing slopes (i.e., not maximized into the terrain). Rainfall
over the 24-hr period will average 2-4" along the Coastal Ranges
and coastline, with higher amounts (3-6+ inches) over southwestern
Oregon. AR will be progressive enough through the day 1 period,
and with the burn scars in the higher terrain where snow will be
the dominant precipitation type, per collaboration with WFOs MFR
and EKA have not upgraded any portion of the Marginal Risk area to
a Slight.

...Eastern Kentucky and Tennessee southwestward into south-central
Louisiana...
Frontal boundary and pre-frontal QLCS will make steady progression eastward/southeastward today. Guidance indicates the best window
of heavier rainfall and rates in the 12Z-00Z window amid gradually
weakening support in moisture, lift, and instability. Recent 7-day
rainfall anomalies are generally negative in the area of the
Marginal Risk (and about 75% of normal) but near and above normal
over portions of Louisiana. There, tail-end convection may fire
and/or re-fire before the front clears the coast and stability
increases. If these storms can materialize, sufficient
moisture/instability and favorably-oriented flow aloft could
result in a few areas of training and excessive rainfall. This
risk is fairly conditional and will depend on upstream convective
evolution. Risk areas will likely need to be adjusted in later
outlooks.

Hurley/Fracasso



Day 2
Valid 12Z Sun Dec 12 2021 - 12Z Mon Dec 13 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS WESTERN
PORTIONS OF CENTRAL AND NORTHERN CALIFORNIA, INCLUDING THE BAY
AREA...

...West Coast...
Strong upper jet streak and vigorous shortwave energy diving
southeastward from the Gulf of Alaska will further amplify the
deep low across the northern Pacific, as the longwave trough
pivots closer to the central-northern West Coast toward the end of
the day 2 forecast period (Sunday night). The amplification of the
upstream trough/downstream ridge will cause the low-mid level flow
to back s-sw once again, allowing the AR pressing southward during
day 2 to re-emerge somewhere along the central CA coast into the
central valleys with precipitable water values around 0.75-1.00"
(+1 to +1.5 sigma).

Models are in better agreement with respect to the orientation,
location, and timing of the Atmospheric River (AR), thus there is
fairly good consensus with the axis of heaviest QPF. Based on the
increased forecast confidence, we have upgraded a portion of
yesterday's Day 3 Marginal Risk to a Slight Risk from the southern
coastal ranges south through the Bay area.
This is where some of the available high-res CAMs, including the
NAM CONUS Nest and FV3, show isolated totals of 3-5".
Probabilities of >50"/hr rainfall rates will be highest within
this area, which encompasses several burn scars from 2020
(including the Hennessey scar).

The latest output from the Center for Western Weather and Water
Extremes (CW3E) shows a low-end 'moderate' or level 3 AR based on
a 5 point scale on Day 2 (12Z Sun 12/12 to 12Z Mon 12/13), with
the maximum integrated water vapor transport or IVT magnitude
forecast just over 500 kg/m/s. Based on the strength of the
dynamical forcing off the coast and potential robust
thermodynamical response, would not be surprised to see an uptick
in the projected AR strength as the event draws near. Multi-day
ensemble trend has been mostly steadily increasing but still
wavering in location owing to upstream timing/evolution
differences (max QPF spread near/north of SFO).

Fracasso/Hurley

Day 3
Valid 12Z Mon Dec 13 2021 - 12Z Tue Dec 14 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS WESTERN
PORTIONS OF CENTRAL CALIFORNIA, INCLUDING THE BAY AREA AND CENTRAL
CALIFORNIA COAST...

...California...
Amplifying mid-upper trough and associated surface front will
approach the central CA coast on day 3 (Mon-Mon night). Max TPW
values remain between 0.75-1.00" (not overly anomalous for mid
December), however low-level moisture transport remains quite
robust as 850 mb southwesterly flow peaks ~50 kts and 850-700 mb
moisture flux anomalies average 3 to 4 standard deviations above
normal. Guidance shows AR orientation backing slightly (SW to NE)
on day 3 in response to the strong offshore height falls between
31-35N. The guidance shows fairly good consensus with the heavy
rainfall axis dropping a little farther south from day 2, across
the Central CA Coast and into the Santa Lucia and Diablo Ranges.
ECMWF, NAM, GFS, GEM, and UKMet all show at least a maximum of 4"
within the Slight Risk area along the Central CA coast into the
Santa Lucia Mountains, with >5" amounts per the NAM, ECMWF and GEM
regional models. A period with rainfall rates exceeding 0.50" will
be likely, especially within the Slight Risk area, which will
enhance the flash flood and debris flow potential. Of particular
concern will be over burn scar areas, including the Willow (2021)
and River (2020) scars.

Hurley


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!un9QUeTS_U3uwLjTDij2H8Tpghixh59piym3dcHBM6BQ= Pb9kjyxRbmXopdS6DIdF7IV6bTFU$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!un9QUeTS_U3uwLjTDij2H8Tpghixh59piym3dcHBM6BQ= Pb9kjyxRbmXopdS6DIdF7CpnHQ2A$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!un9QUeTS_U3uwLjTDij2H8Tpghixh59piym3dcHBM6BQ= Pb9kjyxRbmXopdS6DIdF7OagEqW3$=20


$$




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FOUS30 KWBC 111946
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
245 PM EST Sat Dec 11 2021

Day 1
Valid 16Z Sat Dec 11 2021 - 12Z Sun Dec 12 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WESTERN OREGON AND NORTHWEST CALIFORNIA, AND FROM PARTS OF
SOUTHWEST WEST VIRGINIA/E KENTUCKY/E TENNESSEE INTO N
GEORGIA/ALABAMA...

16z update:
No changes were required given new 12z guidance, and appears to be
on track with initial forecast for the Oregon and northern
California coastal ranges.

Further east, the southwest to northeast oriented line of showers
and thunderstorms continues to march eastward with a general
downward trend in rainfall intensity. This is particularly the
case along the southwest flank in LA/MS as a subtle speed max
lifts northeast and away from the region. Higher FFG values are
less likely to be exceeded, so have trimmed the Marginal to
northern Alabama/northern Georgia where there are still a few
stronger cells and 12z hi-res CAMS suggestive of isolated hourly
totals of 1-1.25" for at least a few more hours. To the north
across the Cumberland Plateau and into SW WV, the cells are
generally weaker but supportive of .75-1" hourly totals as the
lead convective line marches through. Lower FFG values in the
more complex terrain as well as some mid-level lingering
post-frontal showers still have a low end threat for isolated
flash flooding conditions through about 21z as it clears the
western slopes of the Appalachians.=20=20=20=20


Prior Discussion
~~~~~~~~~~~~~~~~~~~~
...Western Oregon and Northwest California...
Atmospheric River event will progress southward along the
Oregon/northern California coast today in advance of a cold front
with precipitable water values around +1 to +1.5 sigma. Right
entrance region of a 130-150kt upper jet will provide large-scale
ascent that will be only somewhat enhanced on upslope flow into
SSW-facing slopes (i.e., not maximized into the terrain). Rainfall
over the 24-hr period will average 2-4" along the Coastal Ranges
and coastline, with higher amounts (3-6+ inches) over southwestern
Oregon. AR will be progressive enough through the day 1 period,
and with the burn scars in the higher terrain where snow will be
the dominant precipitation type, per collaboration with WFOs MFR
and EKA have not upgraded any portion of the Marginal Risk area to
a Slight.

...Eastern Kentucky and Tennessee southwestward into south-central
Louisiana...
Frontal boundary and pre-frontal QLCS will make steady progression eastward/southeastward today. Guidance indicates the best window
of heavier rainfall and rates in the 12Z-00Z window amid gradually
weakening support in moisture, lift, and instability. Recent 7-day
rainfall anomalies are generally negative in the area of the
Marginal Risk (and about 75% of normal) but near and above normal
over portions of Louisiana. There, tail-end convection may fire
and/or re-fire before the front clears the coast and stability
increases. If these storms can materialize, sufficient
moisture/instability and favorably-oriented flow aloft could
result in a few areas of training and excessive rainfall. This
risk is fairly conditional and will depend on upstream convective
evolution. Risk areas will likely need to be adjusted in later
outlooks.

Hurley/Fracasso



Day 2
Valid 12Z Sun Dec 12 2021 - 12Z Mon Dec 13 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS WESTERN
PORTIONS OF CENTRAL AND NORTHERN CALIFORNIA, INCLUDING SAN
FRANCISCO AND MONTERREY BAY AREAS...

21z update:
...West Coast...
An overall trend for slightly faster southward push of the leading
moisture plume late on Sunday into early Monday, results in the
stalling of the plume a tad south toward Santa Cruz/Monterrey Bay.
This results in increased moisture flux to the northern extension
of the Santa Lucia and Sierra de Salinas ranges for the Day 2
period. As a result, the Slight Risk has been expanded southward
to account for this.

The secondary approaching wave late on Monday lifting toward the
central Oregon coast, will bring a secondary moisture surge
further north toward southwest Oregon and northern California.=20
However, freezing levels will have dropped significantly resulting
in snowfall across the higher coastal terrain, leading to highest
potential for excessive rainfall to precisely to coastal
locations. Some Hi-Res CAMs solutions depict some weak
instability due to the steeper lapse rates aloft and suggest some
convective elements particularly near Cape Mendocino. Given
today's rainfall, the Marginal Risk area will be included tightly
to the coast.

Gallina


Prior Discussion
~~~~~~~~~~~~~~~~~
Strong upper jet streak and vigorous shortwave energy diving
southeastward from the Gulf of Alaska will further amplify the
deep low across the northern Pacific, as the longwave trough
pivots closer to the central-northern West Coast toward the end of
the day 2 forecast period (Sunday night). The amplification of the
upstream trough/downstream ridge will cause the low-mid level flow
to back s-sw once again, allowing the AR pressing southward during
day 2 to re-emerge somewhere along the central CA coast into the
central valleys with precipitable water values around 0.75-1.00"
(+1 to +1.5 sigma).

Models are in better agreement with respect to the orientation,
location, and timing of the Atmospheric River (AR), thus there is
fairly good consensus with the axis of heaviest QPF. Based on the
increased forecast confidence, we have upgraded a portion of
yesterday's Day 3 Marginal Risk to a Slight Risk from the southern
coastal ranges south through the Bay area.
This is where some of the available high-res CAMs, including the
NAM CONUS Nest and FV3, show isolated totals of 3-5".
Probabilities of >50"/hr rainfall rates will be highest within
this area, which encompasses several burn scars from 2020
(including the Hennessey scar).

The latest output from the Center for Western Weather and Water
Extremes (CW3E) shows a low-end 'moderate' or level 3 AR based on
a 5 point scale on Day 2 (12Z Sun 12/12 to 12Z Mon 12/13), with
the maximum integrated water vapor transport or IVT magnitude
forecast just over 500 kg/m/s. Based on the strength of the
dynamical forcing off the coast and potential robust
thermodynamical response, would not be surprised to see an uptick
in the projected AR strength as the event draws near. Multi-day
ensemble trend has been mostly steadily increasing but still
wavering in location owing to upstream timing/evolution
differences (max QPF spread near/north of SFO).

Fracasso/Hurley

Day 3

The Day 3 outlook will be updated by 2030Z.


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!t_oe-vn7j_HEW8_toHD8_IJGWBmKcBfsZfeRzER4YB06= gsLlKzCh_zoY8GslQmHVWwkVv9HI$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!t_oe-vn7j_HEW8_toHD8_IJGWBmKcBfsZfeRzER4YB06= gsLlKzCh_zoY8GslQmHVW7q0EGqa$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!t_oe-vn7j_HEW8_toHD8_IJGWBmKcBfsZfeRzER4YB06= gsLlKzCh_zoY8GslQmHVWzYhYPfh$=20


$$




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FOUS30 KWBC 111947
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
246 PM EST Sat Dec 11 2021

Day 1
Valid 16Z Sat Dec 11 2021 - 12Z Sun Dec 12 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WESTERN OREGON AND NORTHWEST CALIFORNIA, AND FROM PARTS OF
SOUTHWEST WEST VIRGINIA/E KENTUCKY/E TENNESSEE INTO N
GEORGIA/ALABAMA...

16z update:
No changes were required given new 12z guidance, and appears to be
on track with initial forecast for the Oregon and northern
California coastal ranges.

Further east, the southwest to northeast oriented line of showers
and thunderstorms continues to march eastward with a general
downward trend in rainfall intensity. This is particularly the
case along the southwest flank in LA/MS as a subtle speed max
lifts northeast and away from the region. Higher FFG values are
less likely to be exceeded, so have trimmed the Marginal to
northern Alabama/northern Georgia where there are still a few
stronger cells and 12z hi-res CAMS suggestive of isolated hourly
totals of 1-1.25" for at least a few more hours. To the north
across the Cumberland Plateau and into SW WV, the cells are
generally weaker but supportive of .75-1" hourly totals as the
lead convective line marches through. Lower FFG values in the
more complex terrain as well as some mid-level lingering
post-frontal showers still have a low end threat for isolated
flash flooding conditions through about 21z as it clears the
western slopes of the Appalachians.=20=20=20=20


Prior Discussion
~~~~~~~~~~~~~~~~~~~~
...Western Oregon and Northwest California...
Atmospheric River event will progress southward along the
Oregon/northern California coast today in advance of a cold front
with precipitable water values around +1 to +1.5 sigma. Right
entrance region of a 130-150kt upper jet will provide large-scale
ascent that will be only somewhat enhanced on upslope flow into
SSW-facing slopes (i.e., not maximized into the terrain). Rainfall
over the 24-hr period will average 2-4" along the Coastal Ranges
and coastline, with higher amounts (3-6+ inches) over southwestern
Oregon. AR will be progressive enough through the day 1 period,
and with the burn scars in the higher terrain where snow will be
the dominant precipitation type, per collaboration with WFOs MFR
and EKA have not upgraded any portion of the Marginal Risk area to
a Slight.

...Eastern Kentucky and Tennessee southwestward into south-central
Louisiana...
Frontal boundary and pre-frontal QLCS will make steady progression eastward/southeastward today. Guidance indicates the best window
of heavier rainfall and rates in the 12Z-00Z window amid gradually
weakening support in moisture, lift, and instability. Recent 7-day
rainfall anomalies are generally negative in the area of the
Marginal Risk (and about 75% of normal) but near and above normal
over portions of Louisiana. There, tail-end convection may fire
and/or re-fire before the front clears the coast and stability
increases. If these storms can materialize, sufficient
moisture/instability and favorably-oriented flow aloft could
result in a few areas of training and excessive rainfall. This
risk is fairly conditional and will depend on upstream convective
evolution. Risk areas will likely need to be adjusted in later
outlooks.

Hurley/Fracasso



Day 2
Valid 12Z Sun Dec 12 2021 - 12Z Mon Dec 13 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS WESTERN
PORTIONS OF CENTRAL AND NORTHERN CALIFORNIA, INCLUDING SAN
FRANCISCO AND MONTERREY BAY AREAS...

21z update:
...West Coast...
An overall trend for slightly faster southward push of the leading
moisture plume late on Sunday into early Monday, results in the
stalling of the plume a tad south toward Santa Cruz/Monterrey Bay.
This results in increased moisture flux to the northern extension
of the Santa Lucia and Sierra de Salinas ranges for the Day 2
period. As a result, the Slight Risk has been expanded southward
to account for this.

The secondary approaching wave late on Monday lifting toward the
central Oregon coast, will bring a secondary moisture surge
further north toward southwest Oregon and northern California.=20
However, freezing levels will have dropped significantly resulting
in snowfall across the higher coastal terrain, leading to highest
potential for excessive rainfall to precisely to coastal
locations. Some Hi-Res CAMs solutions depict some weak
instability due to the steeper lapse rates aloft and suggest some
convective elements particularly near Cape Mendocino. Given
today's rainfall, the Marginal Risk area will be included tightly
to the coast.

Gallina


Prior Discussion
~~~~~~~~~~~~~~~~~
Strong upper jet streak and vigorous shortwave energy diving
southeastward from the Gulf of Alaska will further amplify the
deep low across the northern Pacific, as the longwave trough
pivots closer to the central-northern West Coast toward the end of
the day 2 forecast period (Sunday night). The amplification of the
upstream trough/downstream ridge will cause the low-mid level flow
to back s-sw once again, allowing the AR pressing southward during
day 2 to re-emerge somewhere along the central CA coast into the
central valleys with precipitable water values around 0.75-1.00"
(+1 to +1.5 sigma).

Models are in better agreement with respect to the orientation,
location, and timing of the Atmospheric River (AR), thus there is
fairly good consensus with the axis of heaviest QPF. Based on the
increased forecast confidence, we have upgraded a portion of
yesterday's Day 3 Marginal Risk to a Slight Risk from the southern
coastal ranges south through the Bay area.
This is where some of the available high-res CAMs, including the
NAM CONUS Nest and FV3, show isolated totals of 3-5".
Probabilities of >50"/hr rainfall rates will be highest within
this area, which encompasses several burn scars from 2020
(including the Hennessey scar).

The latest output from the Center for Western Weather and Water
Extremes (CW3E) shows a low-end 'moderate' or level 3 AR based on
a 5 point scale on Day 2 (12Z Sun 12/12 to 12Z Mon 12/13), with
the maximum integrated water vapor transport or IVT magnitude
forecast just over 500 kg/m/s. Based on the strength of the
dynamical forcing off the coast and potential robust
thermodynamical response, would not be surprised to see an uptick
in the projected AR strength as the event draws near. Multi-day
ensemble trend has been mostly steadily increasing but still
wavering in location owing to upstream timing/evolution
differences (max QPF spread near/north of SFO).

Fracasso/Hurley

Day 3
Valid 12Z Mon Dec 13 2021 - 12Z Tue Dec 14 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS WESTERN
PORTIONS OF CENTRAL AND SOUTHERN CALIFORNIA...

21z update:
...California...
At the start of the period, 13.12z, the lead moisture plume should
be nearing peak backing of the low level flow and generally
centered near the Santa Cruz Range which as noted in the Day 2
discussion, has trended a bit south. Likewise, the approaching
secondary wave/moisture surge (limited to ~.75" TPW) is a bit
faster/south and is expected to press the initial cold
front/moisture plume southward accelerating flow to over 50kts at
850mb while increasing flux anomalies to 3 to 4 standard
deviations about 13.21z to the end of the forecast period.=20
Southward progression may reduce duration at any given point south
of the Santa Lucia range, but rates will increase to over .75"
perhaps to 1" in the steepest/south-southwest facing orography.=20
This seems to be case as the plume rounds Point Conception
overnight Tuesday. Overall trends see an increase of QPF across
the Western Transverse Ranges of Santa Barbara and Ventura
counties before 14.12z. Given this and in coordination with WFO
Oxnard, we have added a Slight Risk to the this area.

Gallina


Prior Discussion
~~~~~~~~~~~~~~~~~~~~~
Amplifying mid-upper trough and associated surface front will
approach the central CA coast on day 3 (Mon-Mon night). Max TPW
values remain between 0.75-1.00" (not overly anomalous for mid
December), however low-level moisture transport remains quite
robust as 850 mb southwesterly flow peaks ~50 kts and 850-700 mb
moisture flux anomalies average 3 to 4 standard deviations above
normal. Guidance shows AR orientation backing slightly (SW to NE)
on day 3 in response to the strong offshore height falls between
31-35N. The guidance shows fairly good consensus with the heavy
rainfall axis dropping a little farther south from day 2, across
the Central CA Coast and into the Santa Lucia and Diablo Ranges.
ECMWF, NAM, GFS, GEM, and UKMet all show at least a maximum of 4"
within the Slight Risk area along the Central CA coast into the
Santa Lucia Mountains, with >5" amounts per the NAM, ECMWF and GEM
regional models. A period with rainfall rates exceeding 0.50" will
be likely, especially within the Slight Risk area, which will
enhance the flash flood and debris flow potential. Of particular
concern will be over burn scar areas, including the Willow (2021)
and River (2020) scars.

Hurley


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!uUomjwxRCB_xrWtd0Cvj1oSG0e-RbdvZS_MOHQHMxUtm= LsBFbg1HQKwe69CjYUWiUlprH4Q1$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!uUomjwxRCB_xrWtd0Cvj1oSG0e-RbdvZS_MOHQHMxUtm= LsBFbg1HQKwe69CjYUWiUulMY053$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!uUomjwxRCB_xrWtd0Cvj1oSG0e-RbdvZS_MOHQHMxUtm= LsBFbg1HQKwe69CjYUWiUiFRWhhW$=20


$$




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FOUS30 KWBC 121537
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1034 AM EST Sun Dec 12 2021

Day 1
Valid 12Z Sun Dec 12 2021 - 12Z Mon Dec 13 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS WESTERN
PORTIONS OF CENTRAL AND NORTHERN CALIFORNIA, INCLUDING SAN
FRANCISCO AND MONTERREY BAY AREAS...

16z update:
...California...
Leading primary axis of moisture core is currently centered
along/south of the mouth of San Francisco Bay, so have made some
small adjustments to the northern edges of Slight Risk area for
North Bay counties and was considering removing the Marginal Risk
for the dry slot gap ahead of the secondary moisture surge
associated with next shortwave/height-falls approaching by the end
of the forecast period. However, the 12z Hi-Res CAMs show some
timing differences that may keep central and southern Mendocino
and Sonoma counties in play for some scattered showers/increased
moisture flux by 13.12z to not get too precise in drawing this
gap; even though it is more likely to be post-13.12z into the day
2 period. Otherwise further south, the timing/placement appears
to be on target from prior thinking with only a slight trend for
increased rainfall rates (.5-.75"/hr) with 90%+ HREF probability
of 24hr totals of 3" (~30% for 5"+) for the Santa Cruz Mountains;
however, the increase is not substantial in comparison to prior
cycles to warrant an increase in category.=20=20

Gallina


Prior Discussion
~~~~~~~~~~~~~~~~~~~
Strong upper jet streak and vigorous shortwave energy diving
southeastward from the Gulf of Alaska will further amplify the
deep low across the northern Pacific, as the longwave trough
pivots closer to the central-northern West Coast toward the end of
the day 1 forecast period (Sunday night). The amplification of the
upstream trough/downstream ridge will cause the low-mid level flow
to back s-sw once again, allowing the AR to buckle and exhibit a
slower southward progression in the vicinity of Santa
Cruz/Monterrey Bay by Sunday evening. During the latter half of
the day 1 period (00-12Z Mon), the low level moisture transport
picks up a bit (850 mb moisture flux anomalies climb to +3
standard deviations above normal), which given the
quasi-stationary nature of the AR with TPW values ~1.00", will
allow for a prolonged period of high probabilities of >0.50"/hr
rainfall rates per the HREF (between 06-12Z) within the Slight
Risk area, which encompasses several burn scars from 2020
(including the Hennessey scar). Given the strong upslope
component, per the high-res CAMs localized rainfall total between
4-8" will be possible along the windward slopes of the Santa Cruz
and Santa Lucia Mountains.

The secondary approaching wave late on Monday lifting toward the
central Oregon coast, will bring a secondary moisture surge
further north toward southwest Oregon and northern California.
However, freezing levels will have dropped significantly resulting
in snowfall across the higher coastal terrain, leading to highest
potential for excessive rainfall to precisely to coastal
locations. Some Hi-Res CAMs solutions depict some weak instability
due to the steeper lapse rates aloft and suggest some convective
elements particularly near Cape Mendocino. Given yesterday's
rainfall, the Marginal Risk area will be included tightly to the
coast.

Hurley





Day 2
Valid 12Z Mon Dec 13 2021 - 12Z Tue Dec 14 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS WESTERN
PORTIONS OF CENTRAL AND SOUTHERN CALIFORNIA...

...California...
Amplifying mid-upper trough and associated surface front will
approach the central CA coast on day 2 (Mon-Mon night). Max TPW
values remain between 0.75-1.00" (not overly anomalous for mid
December), however low-level moisture transport remains quite
robust as 850 mb southwesterly flow peaks between 55-65 kts and
850-700 mb moisture flux anomalies average 4 to 4.5 standard
deviations above normal. Guidance shows AR orientation backing
slightly (SW to NE) on day 2 in response to the strong offshore
height falls between 31-35N. The guidance continues to show a
couple of QPF maxima -- one over the southern (upwind) slopes of
the Santa Cruz mountains and another more pronounced max over the
northern slopes of the Santa Lucia Ranges (in the vicinity of
Pfeiffer Big Sur State Park). A few operational models show 24hr
rainfall amounts >6" over the Northern Santa Lucias, including the
ECMWF and GEM Regional. Hourly QPF progs from the 00Z NAM CONUS
Nest shows a prolonged period of 0.50-0.75" hourly rainfall rates
over these Slight Risk areas, with peak hourly rates between
0.75-1.00" over the northern Santa Lucias after 18Z Monday. Of
particular concern from a flash flooding and debris flow risk
standpoint will be across the recent burn scar areas --
specifically those from the Willow (2021), River (2020), and Dolan
(2020) fires.=20

Farther south, by Monday night the favorable orographic component
will allow the heavier rates (0.50+ inch/hr) to spread across the
Transverse Ranges and southern slopes from Point Conception east
to Santa Barbara and areas just north of Ventura. As a result, a
separate Slight Risk added to yesterday's Day 3 ERO will remain in
today's Day 2 outlook.

Hurley

Day 3
Valid 12Z Tue Dec 14 2021 - 12Z Wed Dec 15 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTHWEST
PORTIONS OF CALIFORNIA, INCLUDING THE LOS ANGELES AND SAN DIEGO
METRO AREAS...

..Central-Southern California...
Full-latitude trough/strong height falls and accompanying surface
cold front will finally pivot through southern CA during the
latter part of Day 3 (late Tuesday). Until then however, the AR
and associated robust low-mid level moisture transport will shift
southward through southwest CA, bringing a bout of heavy orograhpically-enhanced rain and mountain snows along and upwind
of the Transverse and Peninsular ranges. Rapidly dropping snow
levels after 00Z Wed will mitigate the flash flood and debris flow
threat above 4000 ft, which would include several of the 2020-21
burn scar areas. The Slight Risk from Day 2 was pulled farther
south on Day 3, with some overlap with the Slight on Day 2 over
the Transverse Ranges, as the AR drops across southern CA early in
the period before accelerating south of the border after 00Z Wed.
Hourly rainfall rates around or above 0.50" within the AR plume
will remain possible, and as such will pose a flash flood threat
across the LA and SD metro areas along with burn scar areas in
nearby foothills.=20=20=20

Hurley


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!uDjc_WrQX9rdjEmzahSF6bA1ZAYzm_BWqBL0marF87gx= hOtfmLiQ09gz9lrq1fVEfDAqv6gm$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!uDjc_WrQX9rdjEmzahSF6bA1ZAYzm_BWqBL0marF87gx= hOtfmLiQ09gz9lrq1fVEfGWytS6y$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!uDjc_WrQX9rdjEmzahSF6bA1ZAYzm_BWqBL0marF87gx= hOtfmLiQ09gz9lrq1fVEfDiwx6eM$=20


$$




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FOUS30 KWBC 121937
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
236 PM EST Sun Dec 12 2021

Day 1
Valid 16Z Sun Dec 12 2021 - 12Z Mon Dec 13 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS WESTERN
PORTIONS OF CENTRAL AND NORTHERN CALIFORNIA, INCLUDING SAN
FRANCISCO AND MONTERREY BAY AREAS...

16z update:
...California...
Leading primary axis of moisture core is currently centered
along/south of the mouth of San Francisco Bay, so have made some
small adjustments to the northern edges of Slight Risk area for
North Bay counties and was considering removing the Marginal Risk
for the dry slot gap ahead of the secondary moisture surge
associated with next shortwave/height-falls approaching by the end
of the forecast period. However, the 12z Hi-Res CAMs show some
timing differences that may keep central and southern Mendocino
and Sonoma counties in play for some scattered showers/increased
moisture flux by 13.12z to not get too precise in drawing this
gap; even though it is more likely to be post-13.12z into the day
2 period. Otherwise further south, the timing/placement appears
to be on target from prior thinking with only a slight trend for
increased rainfall rates (.5-.75"/hr) with 90%+ HREF probability
of 24hr totals of 3" (~30% for 5"+) for the Santa Cruz Mountains;
however, the increase is not substantial in comparison to prior
cycles to warrant an increase in category.=20=20

Gallina


Prior Discussion
~~~~~~~~~~~~~~~~~~~
Strong upper jet streak and vigorous shortwave energy diving
southeastward from the Gulf of Alaska will further amplify the
deep low across the northern Pacific, as the longwave trough
pivots closer to the central-northern West Coast toward the end of
the day 1 forecast period (Sunday night). The amplification of the
upstream trough/downstream ridge will cause the low-mid level flow
to back s-sw once again, allowing the AR to buckle and exhibit a
slower southward progression in the vicinity of Santa
Cruz/Monterrey Bay by Sunday evening. During the latter half of
the day 1 period (00-12Z Mon), the low level moisture transport
picks up a bit (850 mb moisture flux anomalies climb to +3
standard deviations above normal), which given the
quasi-stationary nature of the AR with TPW values ~1.00", will
allow for a prolonged period of high probabilities of >0.50"/hr
rainfall rates per the HREF (between 06-12Z) within the Slight
Risk area, which encompasses several burn scars from 2020
(including the Hennessey scar). Given the strong upslope
component, per the high-res CAMs localized rainfall total between
4-8" will be possible along the windward slopes of the Santa Cruz
and Santa Lucia Mountains.

The secondary approaching wave late on Monday lifting toward the
central Oregon coast, will bring a secondary moisture surge
further north toward southwest Oregon and northern California.
However, freezing levels will have dropped significantly resulting
in snowfall across the higher coastal terrain, leading to highest
potential for excessive rainfall to precisely to coastal
locations. Some Hi-Res CAMs solutions depict some weak instability
due to the steeper lapse rates aloft and suggest some convective
elements particularly near Cape Mendocino. Given yesterday's
rainfall, the Marginal Risk area will be included tightly to the
coast.

Hurley


Day 2
Valid 12Z Mon Dec 13 2021 - 12Z Tue Dec 14 2021

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE BIG SUR
COAST OF CENTRAL CALIFORNIA...

21z update:
...California...
An additional cycle of Hi-Res CAMs and HREF probabilities for the
entirety of the Day 2 period (13.12z-14.12z) provided higher
confidence toward upgrading a very small area of the Big Sur coast
line where 12z HRRR, ARW, ARW2 and the HREF/NBM ensemble means
suggest 8" totals with HREF probabilities 75% for 8"/24hr along
the Monterey into far northwest San Luis Obispo county and near
100% confidence in over 5", with the lowest totals at 4" by the
UKMET/GFS (large grid scale global models). While the hi-res
ensembles are probably skewed a bit by the 15" totals of the
Nam-Conest, many suggest hourly rates of 1-1.25"/hr particularly
between 15-21z when the two plumes start to merge in the vicinity
of the Santa Lucia Mtns before starting the southward progression
in earnest. Combine this enhancement in proximity to the 2020
Dolan burn scar and in coordination with WFO Monterey & Oxnard, an
upgrade to a Moderate Risk was narrow focused for this portion of
the Big Sur coast of Central California with flash flooding and
mudslide/rock falls becoming increasingly probable.

As the digging shortwave associated with the secondary surge in moisture/forcing drops south, it continues to sharply amplify,
increasing low level flow strength and taking the modest 1" total
TPW plume tightening it increasing to 1.25" and accelerating and
backing the winds more south-southwesterly to 45-50kts at 850mb by
14.00z as it rounds Point Conception. This will bring more favorable/orthogonal moisture flux to the Transverse Range of
Santa Barbara and Ventura counties with similar 1-1.25"/hr
rates/totals. Eastward progression of the plume will limit the
overall totals (2-5") but still continue to present a Slight Risk
of excessive rainfall and flash flooding/debris run-off
particularly out of the Alisal burn scar.

Gallina


Prior Discussion
~~~~~~~~~~~~~~~~~~~
Amplifying mid-upper trough and associated surface front will
approach the central CA coast on day 2 (Mon-Mon night). Max TPW
values remain between 0.75-1.00" (not overly anomalous for mid
December), however low-level moisture transport remains quite
robust as 850 mb southwesterly flow peaks between 55-65 kts and
850-700 mb moisture flux anomalies average 4 to 4.5 standard
deviations above normal. Guidance shows AR orientation backing
slightly (SW to NE) on day 2 in response to the strong offshore
height falls between 31-35N. The guidance continues to show a
couple of QPF maxima -- one over the southern (upwind) slopes of
the Santa Cruz mountains and another more pronounced max over the
northern slopes of the Santa Lucia Ranges (in the vicinity of
Pfeiffer Big Sur State Park). A few operational models show 24hr
rainfall amounts >6" over the Northern Santa Lucias, including the
ECMWF and GEM Regional. Hourly QPF progs from the 00Z NAM CONUS
Nest shows a prolonged period of 0.50-0.75" hourly rainfall rates
over these Slight Risk areas, with peak hourly rates between
0.75-1.00" over the northern Santa Lucias after 18Z Monday. Of
particular concern from a flash flooding and debris flow risk
standpoint will be across the recent burn scar areas --
specifically those from the Willow (2021), River (2020), and Dolan
(2020) fires.=20

Farther south, by Monday night the favorable orographic component
will allow the heavier rates (0.50+ inch/hr) to spread across the
Transverse Ranges and southern slopes from Point Conception east
to Santa Barbara and areas just north of Ventura. As a result, a
separate Slight Risk added to yesterday's Day 3 ERO will remain in
today's Day 2 outlook.

Hurley

Day 3

The Day 3 outlook will be updated by 2030Z.


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!oEUwYK8tLK_8musPPMt9Pfn7roYS0B2FoHDVColWS59C= ypEBqNw1eFmtBDahvzwfnmJDeozl$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!oEUwYK8tLK_8musPPMt9Pfn7roYS0B2FoHDVColWS59C= ypEBqNw1eFmtBDahvzwfnmKKQZpE$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!oEUwYK8tLK_8musPPMt9Pfn7roYS0B2FoHDVColWS59C= ypEBqNw1eFmtBDahvzwfnjgxjhGa$=20


$$




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FOUS30 KWBC 121937
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
237 PM EST Sun Dec 12 2021

Day 1
Valid 16Z Sun Dec 12 2021 - 12Z Mon Dec 13 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS WESTERN
PORTIONS OF CENTRAL AND NORTHERN CALIFORNIA, INCLUDING SAN
FRANCISCO AND MONTERREY BAY AREAS...

16z update:
...California...
Leading primary axis of moisture core is currently centered
along/south of the mouth of San Francisco Bay, so have made some
small adjustments to the northern edges of Slight Risk area for
North Bay counties and was considering removing the Marginal Risk
for the dry slot gap ahead of the secondary moisture surge
associated with next shortwave/height-falls approaching by the end
of the forecast period. However, the 12z Hi-Res CAMs show some
timing differences that may keep central and southern Mendocino
and Sonoma counties in play for some scattered showers/increased
moisture flux by 13.12z to not get too precise in drawing this
gap; even though it is more likely to be post-13.12z into the day
2 period. Otherwise further south, the timing/placement appears
to be on target from prior thinking with only a slight trend for
increased rainfall rates (.5-.75"/hr) with 90%+ HREF probability
of 24hr totals of 3" (~30% for 5"+) for the Santa Cruz Mountains;
however, the increase is not substantial in comparison to prior
cycles to warrant an increase in category.=20=20

Gallina


Prior Discussion
~~~~~~~~~~~~~~~~~~~
Strong upper jet streak and vigorous shortwave energy diving
southeastward from the Gulf of Alaska will further amplify the
deep low across the northern Pacific, as the longwave trough
pivots closer to the central-northern West Coast toward the end of
the day 1 forecast period (Sunday night). The amplification of the
upstream trough/downstream ridge will cause the low-mid level flow
to back s-sw once again, allowing the AR to buckle and exhibit a
slower southward progression in the vicinity of Santa
Cruz/Monterrey Bay by Sunday evening. During the latter half of
the day 1 period (00-12Z Mon), the low level moisture transport
picks up a bit (850 mb moisture flux anomalies climb to +3
standard deviations above normal), which given the
quasi-stationary nature of the AR with TPW values ~1.00", will
allow for a prolonged period of high probabilities of >0.50"/hr
rainfall rates per the HREF (between 06-12Z) within the Slight
Risk area, which encompasses several burn scars from 2020
(including the Hennessey scar). Given the strong upslope
component, per the high-res CAMs localized rainfall total between
4-8" will be possible along the windward slopes of the Santa Cruz
and Santa Lucia Mountains.

The secondary approaching wave late on Monday lifting toward the
central Oregon coast, will bring a secondary moisture surge
further north toward southwest Oregon and northern California.
However, freezing levels will have dropped significantly resulting
in snowfall across the higher coastal terrain, leading to highest
potential for excessive rainfall to precisely to coastal
locations. Some Hi-Res CAMs solutions depict some weak instability
due to the steeper lapse rates aloft and suggest some convective
elements particularly near Cape Mendocino. Given yesterday's
rainfall, the Marginal Risk area will be included tightly to the
coast.

Hurley

Day 2
Valid 12Z Mon Dec 13 2021 - 12Z Tue Dec 14 2021

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE BIG SUR
COAST OF CENTRAL CALIFORNIA...

21z update:
...California...
An additional cycle of Hi-Res CAMs and HREF probabilities for the
entirety of the Day 2 period (13.12z-14.12z) provided higher
confidence toward upgrading a very small area of the Big Sur coast
line where 12z HRRR, ARW, ARW2 and the HREF/NBM ensemble means
suggest 8" totals with HREF probabilities 75% for 8"/24hr along
the Monterey into far northwest San Luis Obispo county and near
100% confidence in over 5", with the lowest totals at 4" by the
UKMET/GFS (large grid scale global models). While the hi-res
ensembles are probably skewed a bit by the 15" totals of the
Nam-Conest, many suggest hourly rates of 1-1.25"/hr particularly
between 15-21z when the two plumes start to merge in the vicinity
of the Santa Lucia Mtns before starting the southward progression
in earnest. Combine this enhancement in proximity to the 2020
Dolan burn scar and in coordination with WFO Monterey & Oxnard, an
upgrade to a Moderate Risk was narrow focused for this portion of
the Big Sur coast of Central California with flash flooding and
mudslide/rock falls becoming increasingly probable.

As the digging shortwave associated with the secondary surge in moisture/forcing drops south, it continues to sharply amplify,
increasing low level flow strength and taking the modest 1" total
TPW plume tightening it increasing to 1.25" and accelerating and
backing the winds more south-southwesterly to 45-50kts at 850mb by
14.00z as it rounds Point Conception. This will bring more favorable/orthogonal moisture flux to the Transverse Range of
Santa Barbara and Ventura counties with similar 1-1.25"/hr
rates/totals. Eastward progression of the plume will limit the
overall totals (2-5") but still continue to present a Slight Risk
of excessive rainfall and flash flooding/debris run-off
particularly out of the Alisal burn scar.

Gallina


Prior Discussion
~~~~~~~~~~~~~~~~~~~
Amplifying mid-upper trough and associated surface front will
approach the central CA coast on day 2 (Mon-Mon night). Max TPW
values remain between 0.75-1.00" (not overly anomalous for mid
December), however low-level moisture transport remains quite
robust as 850 mb southwesterly flow peaks between 55-65 kts and
850-700 mb moisture flux anomalies average 4 to 4.5 standard
deviations above normal. Guidance shows AR orientation backing
slightly (SW to NE) on day 2 in response to the strong offshore
height falls between 31-35N. The guidance continues to show a
couple of QPF maxima -- one over the southern (upwind) slopes of
the Santa Cruz mountains and another more pronounced max over the
northern slopes of the Santa Lucia Ranges (in the vicinity of
Pfeiffer Big Sur State Park). A few operational models show 24hr
rainfall amounts >6" over the Northern Santa Lucias, including the
ECMWF and GEM Regional. Hourly QPF progs from the 00Z NAM CONUS
Nest shows a prolonged period of 0.50-0.75" hourly rainfall rates
over these Slight Risk areas, with peak hourly rates between
0.75-1.00" over the northern Santa Lucias after 18Z Monday. Of
particular concern from a flash flooding and debris flow risk
standpoint will be across the recent burn scar areas --
specifically those from the Willow (2021), River (2020), and Dolan
(2020) fires.=20

Farther south, by Monday night the favorable orographic component
will allow the heavier rates (0.50+ inch/hr) to spread across the
Transverse Ranges and southern slopes from Point Conception east
to Santa Barbara and areas just north of Ventura. As a result, a
separate Slight Risk added to yesterday's Day 3 ERO will remain in
today's Day 2 outlook.

Hurley

Day 3
Valid 12Z Tue Dec 14 2021 - 12Z Wed Dec 15 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTHWEST
PORTIONS OF CALIFORNIA, INCLUDING THE LOS ANGELES AND SAN DIEGO
METRO AREAS...

21z update:
...Southern California...
Global guidance continues to depict a strong shortwave digging
with strong height-falls before starting to swing negative tilt
through southern California by 15.00z. The average to slightly
above average moisture stream in advance of the accompanying cold
front will see some narrowing and concentration of the deep layer
moisture with a combination of backing low level wind response to
the approaching shortwave while a sharp westerly push behind the
cold combining to have nearly 4 standard deviation of moisture
flux associated with the front as it progresses eastward at a good
pace through the California Bight. In fact, the orientation of
the plume initially is fairly orthogonal to the Transverse Ranges
early in the period, but slowly veers to become modestly
orthogonal to the Peninsular Range toward 15.00z, supporting
.7-1"/hr rates initially (per NAM-Conest, GFS and UA WRF) before
reducing to .5"/hr further south and east. Overall totals in the
terrain of 3-5" (higher precipitation amounts in the highest
elevations likely converting to snow even early) with 1-2" in the
lower valley floors continue to support a broad Slight Risk of
Excessive Rainfall from eastern Santa Barbara county to San Diego
county.

...Northwest Arizona/Southwest Utah/Southern Nevada...
The strength of the shortwave going negative tilt across Southern
California into S Nevada, will support increased moisture moving
through or over the Peninsular Range across the deserts of
Southern California with .75" Total PWATs generally maximized over
85-7H. Strong southerly boundary layer flow up the Lower Colorado
River will likely increase moisture but with drier ground and
lower atmospheric conditions in place, the strength of the flux is
likely to generate hourly rates of .25-.5"/hr per GFS/UA WRF
having lost some potential from sub-cloud evaporation for favored
upslope terrain across southeast Nevada, southwest Utah and
northwest Arizona. Even then, rapidly falling freezing levels
would limit rainfall totals to about 1" across these areas. At
this time, conditions are not favorable for an introduction of a
Marginal Risk to this area but trends will be monitored especially
with hi-res CAMs becoming available over the next few cycles.

Gallina/Hurley


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!uX3Q0r4gM8tQu0zWeo_Hc0y3L4skvbGrBDjpSe40NHrd= Gq1F9VWFJh5O6X8XDeZkXTi8Q8tv$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!uX3Q0r4gM8tQu0zWeo_Hc0y3L4skvbGrBDjpSe40NHrd= Gq1F9VWFJh5O6X8XDeZkXQ0AsxgX$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!uX3Q0r4gM8tQu0zWeo_Hc0y3L4skvbGrBDjpSe40NHrd= Gq1F9VWFJh5O6X8XDeZkXaw95OoM$=20


$$




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FOUS30 KWBC 181602
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1101 AM EST Sat Dec 18 2021

Day 1
Valid 16Z Sat Dec 18 2021 - 12Z Sun Dec 19 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN SOUTHEAST
TEXAS/SOUTHWEST LOUISIANA & SOUTHEAST ALABAMA/SOUTHWEST
GEORGIA/FLORIDA PANHANDLE...

...16z update...
...Southeast Alabama and adjacent Florida/Georgia...

CIRA Layered Precipitable Water plots denote an anomalous pocket
of enhanced moisture across the northeast Gulf of Mexico lifting
northward along the western periphery of the subtropical ridge
over the Sargasso Sea. This is particularly noticeable in the
850-7H and 7-5H layers, this results in TPW values of 1.5-1.75". A
slight eastward trend of the timing/placement of subtropical
stream subtle shortwave crossing GA into SC/W NC has draped the 7H
boundary a bit orthogonal to the moisture plume supporting some
increased convergence, while in close proximity to higher theta-E
source of the Gulf. As such, hi-res 12z CAM solutions (including HRRR/ARWs/Nam-Nest) suggest hourly rates of 1.75-2"/hr. 12z HREF
demarcate an increase in heavy rainfall probabilities particularly
across Southeast Alabama and western Panhandle in the 21-03z time
frame. Increased deep layer steering toward the east with the
faster progged exit of the shortwave may support short-term
training or mergers and as a result guidance supports isolated
2-4" totals.=20

Limiting factor (similar to Texas) will continue to be dry soil
conditions, as little rain has fallen over the last month ~5-15%
of normal resulting in 0-40cm soil anomalies in 10-20% range per
NASA SPoRT LIS product. Still, the sheer rate and less
percolation into dry soils could result in increased runoff, and
in conversation with the NWC, the National Water Model suggests a
few locations of rapid onset flooding are possible. As such have
introduced a small Marginal Risk of Excessive Rainfall to account
for this potential.

...Southeast Texas/Southwest Louisiana...
12z Hi-Res CAMs continue to hone in on pre-frontal slow moving
convection developing in higher theta-e, moisture surge off the
western Gulf low level flow with potential for increased rain
rates of 2-2.5"/hr. The greater concern is as the frontal
convection progresses southward, cell mergers and increased
duration for intense rates could pose localized 3-4"+ totals,
particularly in the vicinity of Metro Houston. 12z HREF
probabilities continue to steadily increase and provide confidence
for excessive rainfall with 3"/3hr probabilities at 50% in the
18-00z time frame. Thereafter, the front should progress
offshore. As such, have introduced a small Slight Risk generally
centered over the Metro.


...Central Oregon Coastal Range...
A solid but not highly anomalous Atmospheric river is currently in
progress over the Olympic Range of western Washington into the
Northern Cascades. Integrated Vapor Transport (IVT) values of 750
kg/m/s are solid going into Washington, but given the shortwave
continues to be progressing tracking through Washington into the
northern US Rockies/southern Canadian Rockies by 12z, the
magnitudes of higher QPF are generally above freezing levels
resulting in heavier snow than potential excessive
rainfall/run-off.=20=20

However, as the front sags south into northern and central Coastal
Range of Oregon, the plume starts to stall under weakening
influence of the exiting wave but strengthening influence of the strengthening/deepening upstream wave and increased southerly
flow. Winds will slacken and IVT values will drop to about
400-500 kg/m/s as PW values drop to below 1". Rain rates will
also be below .5"/hr but still support longer duration moderate
rainfall with totals of 1-2.5" in the Coastal Range (below
freezing levels) prior to 19.12z. AHPS precipitation anomalies
are above average but soil conditions are normal per NASA SPoRT
LIS 0-40cm product. So, at this time have not introduced a
Marginal Risk of excessive rainfall, though it is close, but in
continuation into the D2 period, it will need to be further
evaluated.=20

Gallina


Prior Discussion
~~~~~~~~~~~~~~~~~~~
...Southeast Texas/Southwest Louisiana...
A cold front will sweep southeast quickly in the western Gulf
Coast region today, likely moving offshore of Texas by 00Z, and
Louisiana shortly thereafter. Therefore, the threat of heavy
rainfall from convection along and ahead of the front will be
concentrated in the first half of the forecast period, although it
should be focused most acutely around the time of the frontal
passage. The environment will be generally supportive of high
instantaneous rain rates and organized convective lines and
clusters, with precipitable water values around 1.6 to 1.8 inches
(above the 95th percentile for December) and MUCAPE around
1000-1500 j/kg (above the 90th percentile for December). Indeed,
multiple HREF members show 2+ inch per hour rain rates, and the
06Z HRRR indicates 15-minute rain rates potentially reaching 1
inch in the strongest convection.

The main limiting factors for flash flood impacts will be the
progressive nature of the front, which should limit the residence
time of intense rain in any one location, and the dry antecedent
conditions with 30-day rainfall around half the average value at a
normally drier time of year. Therefore, the most likely location
for impacts would be in any urbanized areas, particularly the
Houston metro area, where even short bursts of very intense
rainfall could produce excessive runoff. However, given the
aforementioned limiting factors, the Marginal Risk that was
already in effect has been maintained. If confidence grows in
heavy rain rates being sustained for more than an hour in the
Houston metro area, it's possible a localized upgrade to Slight
Risk could be warranted.

Lamers


Day 2
Valid 12Z Sun Dec 19 2021 - 12Z Mon Dec 20 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Lamers

Day 3
Valid 12Z Mon Dec 20 2021 - 12Z Tue Dec 21 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Lamers


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!t2Mld_m89doykJLTiSkmJDV7LDyr-ZoW93DMapfs6ppk= 5s31h67kXvnSzBlX5hWOtFLLpbHq$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!t2Mld_m89doykJLTiSkmJDV7LDyr-ZoW93DMapfs6ppk= 5s31h67kXvnSzBlX5hWOtLDvl-1J$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!t2Mld_m89doykJLTiSkmJDV7LDyr-ZoW93DMapfs6ppk= 5s31h67kXvnSzBlX5hWOtBIZaNDf$=20


$$




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FOUS30 KWBC 181603
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1103 AM EST Sat Dec 18 2021

Day 1
Valid 16Z Sat Dec 18 2021 - 12Z Sun Dec 19 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN SOUTHEAST
TEXAS...

...16z update...
...Southeast Alabama and adjacent Florida/Georgia...

CIRA Layered Precipitable Water plots denote an anomalous pocket
of enhanced moisture across the northeast Gulf of Mexico lifting
northward along the western periphery of the subtropical ridge
over the Sargasso Sea. This is particularly noticeable in the
850-7H and 7-5H layers, this results in TPW values of 1.5-1.75". A
slight eastward trend of the timing/placement of subtropical
stream subtle shortwave crossing GA into SC/W NC has draped the 7H
boundary a bit orthogonal to the moisture plume supporting some
increased convergence, while in close proximity to higher theta-E
source of the Gulf. As such, hi-res 12z CAM solutions (including HRRR/ARWs/Nam-Nest) suggest hourly rates of 1.75-2"/hr. 12z HREF
demarcate an increase in heavy rainfall probabilities particularly
across Southeast Alabama and western Panhandle in the 21-03z time
frame. Increased deep layer steering toward the east with the
faster progged exit of the shortwave may support short-term
training or mergers and as a result guidance supports isolated
2-4" totals.=20

Limiting factor (similar to Texas) will continue to be dry soil
conditions, as little rain has fallen over the last month ~5-15%
of normal resulting in 0-40cm soil anomalies in 10-20% range per
NASA SPoRT LIS product. Still, the sheer rate and less
percolation into dry soils could result in increased runoff, and
in conversation with the NWC, the National Water Model suggests a
few locations of rapid onset flooding are possible. As such have
introduced a small Marginal Risk of Excessive Rainfall to account
for this potential.

...Southeast Texas/Southwest Louisiana...
12z Hi-Res CAMs continue to hone in on pre-frontal slow moving
convection developing in higher theta-e, moisture surge off the
western Gulf low level flow with potential for increased rain
rates of 2-2.5"/hr. The greater concern is as the frontal
convection progresses southward, cell mergers and increased
duration for intense rates could pose localized 3-4"+ totals,
particularly in the vicinity of Metro Houston. 12z HREF
probabilities continue to steadily increase and provide confidence
for excessive rainfall with 3"/3hr probabilities at 50% in the
18-00z time frame. Thereafter, the front should progress
offshore. As such, have introduced a small Slight Risk generally
centered over the Metro.


...Central Oregon Coastal Range...
A solid but not highly anomalous Atmospheric river is currently in
progress over the Olympic Range of western Washington into the
Northern Cascades. Integrated Vapor Transport (IVT) values of 750
kg/m/s are solid going into Washington, but given the shortwave
continues to be progressing tracking through Washington into the
northern US Rockies/southern Canadian Rockies by 12z, the
magnitudes of higher QPF are generally above freezing levels
resulting in heavier snow than potential excessive
rainfall/run-off.=20=20

However, as the front sags south into northern and central Coastal
Range of Oregon, the plume starts to stall under weakening
influence of the exiting wave but strengthening influence of the strengthening/deepening upstream wave and increased southerly
flow. Winds will slacken and IVT values will drop to about
400-500 kg/m/s as PW values drop to below 1". Rain rates will
also be below .5"/hr but still support longer duration moderate
rainfall with totals of 1-2.5" in the Coastal Range (below
freezing levels) prior to 19.12z. AHPS precipitation anomalies
are above average but soil conditions are normal per NASA SPoRT
LIS 0-40cm product. So, at this time have not introduced a
Marginal Risk of excessive rainfall, though it is close, but in
continuation into the D2 period, it will need to be further
evaluated.=20

Gallina


Prior Discussion
~~~~~~~~~~~~~~~~~~~
...Southeast Texas/Southwest Louisiana...
A cold front will sweep southeast quickly in the western Gulf
Coast region today, likely moving offshore of Texas by 00Z, and
Louisiana shortly thereafter. Therefore, the threat of heavy
rainfall from convection along and ahead of the front will be
concentrated in the first half of the forecast period, although it
should be focused most acutely around the time of the frontal
passage. The environment will be generally supportive of high
instantaneous rain rates and organized convective lines and
clusters, with precipitable water values around 1.6 to 1.8 inches
(above the 95th percentile for December) and MUCAPE around
1000-1500 j/kg (above the 90th percentile for December). Indeed,
multiple HREF members show 2+ inch per hour rain rates, and the
06Z HRRR indicates 15-minute rain rates potentially reaching 1
inch in the strongest convection.

The main limiting factors for flash flood impacts will be the
progressive nature of the front, which should limit the residence
time of intense rain in any one location, and the dry antecedent
conditions with 30-day rainfall around half the average value at a
normally drier time of year. Therefore, the most likely location
for impacts would be in any urbanized areas, particularly the
Houston metro area, where even short bursts of very intense
rainfall could produce excessive runoff. However, given the
aforementioned limiting factors, the Marginal Risk that was
already in effect has been maintained. If confidence grows in
heavy rain rates being sustained for more than an hour in the
Houston metro area, it's possible a localized upgrade to Slight
Risk could be warranted.

Lamers


Day 2
Valid 12Z Sun Dec 19 2021 - 12Z Mon Dec 20 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Lamers

Day 3
Valid 12Z Mon Dec 20 2021 - 12Z Tue Dec 21 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Lamers


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!smF-iXgjIGpp0Nzbl-MNGTg_j4y4zwy20aFJLtQGJUBQ= czaPQ1EcHtSwIe8AT2iRLhmpjnxA$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!smF-iXgjIGpp0Nzbl-MNGTg_j4y4zwy20aFJLtQGJUBQ= czaPQ1EcHtSwIe8AT2iRLo8AwHF-$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!smF-iXgjIGpp0Nzbl-MNGTg_j4y4zwy20aFJLtQGJUBQ= czaPQ1EcHtSwIe8AT2iRLkt7u8py$=20


$$




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FOUS30 KWBC 181846
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
145 PM EST Sat Dec 18 2021

Day 1
Valid 16Z Sat Dec 18 2021 - 12Z Sun Dec 19 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN SOUTHEAST
TEXAS...

...16z update...
...Southeast Alabama and adjacent Florida/Georgia...

CIRA Layered Precipitable Water plots denote an anomalous pocket
of enhanced moisture across the northeast Gulf of Mexico lifting
northward along the western periphery of the subtropical ridge
over the Sargasso Sea. This is particularly noticeable in the
850-7H and 7-5H layers, this results in TPW values of 1.5-1.75". A
slight eastward trend of the timing/placement of subtropical
stream subtle shortwave crossing GA into SC/W NC has draped the 7H
boundary a bit orthogonal to the moisture plume supporting some
increased convergence, while in close proximity to higher theta-E
source of the Gulf. As such, hi-res 12z CAM solutions (including HRRR/ARWs/Nam-Nest) suggest hourly rates of 1.75-2"/hr. 12z HREF
demarcate an increase in heavy rainfall probabilities particularly
across Southeast Alabama and western Panhandle in the 21-03z time
frame. Increased deep layer steering toward the east with the
faster progged exit of the shortwave may support short-term
training or mergers and as a result guidance supports isolated
2-4" totals.=20

Limiting factor (similar to Texas) will continue to be dry soil
conditions, as little rain has fallen over the last month ~5-15%
of normal resulting in 0-40cm soil anomalies in 10-20% range per
NASA SPoRT LIS product. Still, the sheer rate and less
percolation into dry soils could result in increased runoff, and
in conversation with the NWC, the National Water Model suggests a
few locations of rapid onset flooding are possible. As such have
introduced a small Marginal Risk of Excessive Rainfall to account
for this potential.

...Southeast Texas/Southwest Louisiana...
12z Hi-Res CAMs continue to hone in on pre-frontal slow moving
convection developing in higher theta-e, moisture surge off the
western Gulf low level flow with potential for increased rain
rates of 2-2.5"/hr. The greater concern is as the frontal
convection progresses southward, cell mergers and increased
duration for intense rates could pose localized 3-4"+ totals,
particularly in the vicinity of Metro Houston. 12z HREF
probabilities continue to steadily increase and provide confidence
for excessive rainfall with 3"/3hr probabilities at 50% in the
18-00z time frame. Thereafter, the front should progress
offshore. As such, have introduced a small Slight Risk generally
centered over the Metro.


...Central Oregon Coastal Range...
A solid but not highly anomalous Atmospheric river is currently in
progress over the Olympic Range of western Washington into the
Northern Cascades. Integrated Vapor Transport (IVT) values of 750
kg/m/s are solid going into Washington, but given the shortwave
continues to be progressing tracking through Washington into the
northern US Rockies/southern Canadian Rockies by 12z, the
magnitudes of higher QPF are generally above freezing levels
resulting in heavier snow than potential excessive
rainfall/run-off.=20=20

However, as the front sags south into northern and central Coastal
Range of Oregon, the plume starts to stall under weakening
influence of the exiting wave but strengthening influence of the strengthening/deepening upstream wave and increased southerly
flow. Winds will slacken and IVT values will drop to about
400-500 kg/m/s as PW values drop to below 1". Rain rates will
also be below .5"/hr but still support longer duration moderate
rainfall with totals of 1-2.5" in the Coastal Range (below
freezing levels) prior to 19.12z. AHPS precipitation anomalies
are above average but soil conditions are normal per NASA SPoRT
LIS 0-40cm product. So, at this time have not introduced a
Marginal Risk of excessive rainfall, though it is close, but in
continuation into the D2 period, it will need to be further
evaluated.=20

Gallina


Prior Discussion
~~~~~~~~~~~~~~~~~~~
...Southeast Texas/Southwest Louisiana...
A cold front will sweep southeast quickly in the western Gulf
Coast region today, likely moving offshore of Texas by 00Z, and
Louisiana shortly thereafter. Therefore, the threat of heavy
rainfall from convection along and ahead of the front will be
concentrated in the first half of the forecast period, although it
should be focused most acutely around the time of the frontal
passage. The environment will be generally supportive of high
instantaneous rain rates and organized convective lines and
clusters, with precipitable water values around 1.6 to 1.8 inches
(above the 95th percentile for December) and MUCAPE around
1000-1500 j/kg (above the 90th percentile for December). Indeed,
multiple HREF members show 2+ inch per hour rain rates, and the
06Z HRRR indicates 15-minute rain rates potentially reaching 1
inch in the strongest convection.

The main limiting factors for flash flood impacts will be the
progressive nature of the front, which should limit the residence
time of intense rain in any one location, and the dry antecedent
conditions with 30-day rainfall around half the average value at a
normally drier time of year. Therefore, the most likely location
for impacts would be in any urbanized areas, particularly the
Houston metro area, where even short bursts of very intense
rainfall could produce excessive runoff. However, given the
aforementioned limiting factors, the Marginal Risk that was
already in effect has been maintained. If confidence grows in
heavy rain rates being sustained for more than an hour in the
Houston metro area, it's possible a localized upgrade to Slight
Risk could be warranted.

Lamers


Day 2
Valid 12Z Sun Dec 19 2021 - 12Z Mon Dec 20 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG THE
CENTRAL OREGON COASTAL RANGES...

At the start of the forecast period, 19.12z, the tail end of the
cold front from a quickly exiting shortwave across the US/Canadian
boarder Rockies will have started to stall into a stationary front
crossing the Central Oregon coast between Tillamook and N Coos
county. Deep layer moisture westerly flow will be slacking a bit,
bringing Integrated Vapor Transport (IVT) values to weak to modest
levels around 400-500 kg/m/s. Broadening shield of modest rain
rates of .1-.2"/hr will exist across much of the area of concern,
though rates of .25-.33"/hr are possible with weak vertical
convective development due to proximity to the front itself.=20
However, large scale troughing further southwest will rapidly
deepen a surface cyclone, but will shed a weak mid-level shortwave
feature northeast toward the OR coast. This will spur weak
cyclogenesis and back and strengthen low level flow from 30 to 50+
kts by early morning. This increase in flow will bring higher
total PWats back to near 1" and IVT values in the 750 kg/m/s range
per GEFS/ECENS members. The front will lift northward as a warm
front, but given overall depth of mid-level steering flow, some
shallow convective elements have the potential to intersect the
coast in similar placement to heavier rainfall from the Day 1 time
period (18.12z-19.12z) where 1-2.5" are expected to fall.=20

Steadily increasing rain-rates up to .5"/hr are possible
particularly between 18z and 03z for the central Oregon Coastal
Range. HREF probabilities reach peaks of 50-60% in this time frame
for rates of .33"/hr or 1"/3hr. As the wave moves through, global
guidance (NAM, GFS, UKMET, CMC, ECMWF) suggest and additional 2-4"
bringing 48hr totals across the region to 3-6". Hi-Res CAMs, to
be expected, are a tad higher for south-southwestward facing
orography. As such. As noted in Day 1 ERO discussion, the soil
conditions are generally average, but the two day combination has
some potential for excessive rainfall/flooding with
mudslides/debris flows particularly near burn scars. As such, a
Marginal Risk of Excessive Rainfall was introduced, with
coordination from local forecast offices, for the central Oregon
coastal region.

While the strength of the moisture flux, wind flow resulting in
orographic ascent is much lower across the lower slopes of the
Oregon Cascade region, increased overall rainfall totals
throughout the 48hr period to 2-4", perhaps higher across numerous
large burn scars from the 2020 and 2021 seasons resulted in
expanding the Marginal Risk across to the lower slopes, below
freezing levels in the central Oregon Cascade Range.


Gallina




Day 3

The Day 3 outlook will be updated by 2030Z.


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!s8WErSLQLATtBgiwq2n_fQ6NJUj2PaN3UK8u_D2qI5aY= oTpKHrMBIyDijZoaYlLUhYpiQxfQ$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!s8WErSLQLATtBgiwq2n_fQ6NJUj2PaN3UK8u_D2qI5aY= oTpKHrMBIyDijZoaYlLUhXWRQEZz$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!s8WErSLQLATtBgiwq2n_fQ6NJUj2PaN3UK8u_D2qI5aY= oTpKHrMBIyDijZoaYlLUhVOw3EpM$=20


$$




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FOUS30 KWBC 181847
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
146 PM EST Sat Dec 18 2021

Day 1
Valid 16Z Sat Dec 18 2021 - 12Z Sun Dec 19 2021

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN SOUTHEAST
TEXAS...

...16z update...
...Southeast Alabama and adjacent Florida/Georgia...

CIRA Layered Precipitable Water plots denote an anomalous pocket
of enhanced moisture across the northeast Gulf of Mexico lifting
northward along the western periphery of the subtropical ridge
over the Sargasso Sea. This is particularly noticeable in the
850-7H and 7-5H layers, this results in TPW values of 1.5-1.75". A
slight eastward trend of the timing/placement of subtropical
stream subtle shortwave crossing GA into SC/W NC has draped the 7H
boundary a bit orthogonal to the moisture plume supporting some
increased convergence, while in close proximity to higher theta-E
source of the Gulf. As such, hi-res 12z CAM solutions (including HRRR/ARWs/Nam-Nest) suggest hourly rates of 1.75-2"/hr. 12z HREF
demarcate an increase in heavy rainfall probabilities particularly
across Southeast Alabama and western Panhandle in the 21-03z time
frame. Increased deep layer steering toward the east with the
faster progged exit of the shortwave may support short-term
training or mergers and as a result guidance supports isolated
2-4" totals.=20

Limiting factor (similar to Texas) will continue to be dry soil
conditions, as little rain has fallen over the last month ~5-15%
of normal resulting in 0-40cm soil anomalies in 10-20% range per
NASA SPoRT LIS product. Still, the sheer rate and less
percolation into dry soils could result in increased runoff, and
in conversation with the NWC, the National Water Model suggests a
few locations of rapid onset flooding are possible. As such have
introduced a small Marginal Risk of Excessive Rainfall to account
for this potential.

...Southeast Texas/Southwest Louisiana...
12z Hi-Res CAMs continue to hone in on pre-frontal slow moving
convection developing in higher theta-e, moisture surge off the
western Gulf low level flow with potential for increased rain
rates of 2-2.5"/hr. The greater concern is as the frontal
convection progresses southward, cell mergers and increased
duration for intense rates could pose localized 3-4"+ totals,
particularly in the vicinity of Metro Houston. 12z HREF
probabilities continue to steadily increase and provide confidence
for excessive rainfall with 3"/3hr probabilities at 50% in the
18-00z time frame. Thereafter, the front should progress
offshore. As such, have introduced a small Slight Risk generally
centered over the Metro.


...Central Oregon Coastal Range...
A solid but not highly anomalous Atmospheric river is currently in
progress over the Olympic Range of western Washington into the
Northern Cascades. Integrated Vapor Transport (IVT) values of 750
kg/m/s are solid going into Washington, but given the shortwave
continues to be progressing tracking through Washington into the
northern US Rockies/southern Canadian Rockies by 12z, the
magnitudes of higher QPF are generally above freezing levels
resulting in heavier snow than potential excessive
rainfall/run-off.=20=20

However, as the front sags south into northern and central Coastal
Range of Oregon, the plume starts to stall under weakening
influence of the exiting wave but strengthening influence of the strengthening/deepening upstream wave and increased southerly
flow. Winds will slacken and IVT values will drop to about
400-500 kg/m/s as PW values drop to below 1". Rain rates will
also be below .5"/hr but still support longer duration moderate
rainfall with totals of 1-2.5" in the Coastal Range (below
freezing levels) prior to 19.12z. AHPS precipitation anomalies
are above average but soil conditions are normal per NASA SPoRT
LIS 0-40cm product. So, at this time have not introduced a
Marginal Risk of excessive rainfall, though it is close, but in
continuation into the D2 period, it will need to be further
evaluated.=20

Gallina


Prior Discussion
~~~~~~~~~~~~~~~~~~~
...Southeast Texas/Southwest Louisiana...
A cold front will sweep southeast quickly in the western Gulf
Coast region today, likely moving offshore of Texas by 00Z, and
Louisiana shortly thereafter. Therefore, the threat of heavy
rainfall from convection along and ahead of the front will be
concentrated in the first half of the forecast period, although it
should be focused most acutely around the time of the frontal
passage. The environment will be generally supportive of high
instantaneous rain rates and organized convective lines and
clusters, with precipitable water values around 1.6 to 1.8 inches
(above the 95th percentile for December) and MUCAPE around
1000-1500 j/kg (above the 90th percentile for December). Indeed,
multiple HREF members show 2+ inch per hour rain rates, and the
06Z HRRR indicates 15-minute rain rates potentially reaching 1
inch in the strongest convection.

The main limiting factors for flash flood impacts will be the
progressive nature of the front, which should limit the residence
time of intense rain in any one location, and the dry antecedent
conditions with 30-day rainfall around half the average value at a
normally drier time of year. Therefore, the most likely location
for impacts would be in any urbanized areas, particularly the
Houston metro area, where even short bursts of very intense
rainfall could produce excessive runoff. However, given the
aforementioned limiting factors, the Marginal Risk that was
already in effect has been maintained. If confidence grows in
heavy rain rates being sustained for more than an hour in the
Houston metro area, it's possible a localized upgrade to Slight
Risk could be warranted.

Lamers


Day 2
Valid 12Z Sun Dec 19 2021 - 12Z Mon Dec 20 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG THE
CENTRAL OREGON COASTAL RANGES...

At the start of the forecast period, 19.12z, the tail end of the
cold front from a quickly exiting shortwave across the US/Canadian
boarder Rockies will have started to stall into a stationary front
crossing the Central Oregon coast between Tillamook and N Coos
county. Deep layer moisture westerly flow will be slacking a bit,
bringing Integrated Vapor Transport (IVT) values to weak to modest
levels around 400-500 kg/m/s. Broadening shield of modest rain
rates of .1-.2"/hr will exist across much of the area of concern,
though rates of .25-.33"/hr are possible with weak vertical
convective development due to proximity to the front itself.=20
However, large scale troughing further southwest will rapidly
deepen a surface cyclone, but will shed a weak mid-level shortwave
feature northeast toward the OR coast. This will spur weak
cyclogenesis and back and strengthen low level flow from 30 to 50+
kts by early morning. This increase in flow will bring higher
total PWats back to near 1" and IVT values in the 750 kg/m/s range
per GEFS/ECENS members. The front will lift northward as a warm
front, but given overall depth of mid-level steering flow, some
shallow convective elements have the potential to intersect the
coast in similar placement to heavier rainfall from the Day 1 time
period (18.12z-19.12z) where 1-2.5" are expected to fall.=20

Steadily increasing rain-rates up to .5"/hr are possible
particularly between 18z and 03z for the central Oregon Coastal
Range. HREF probabilities reach peaks of 50-60% in this time frame
for rates of .33"/hr or 1"/3hr. As the wave moves through, global
guidance (NAM, GFS, UKMET, CMC, ECMWF) suggest and additional 2-4"
bringing 48hr totals across the region to 3-6". Hi-Res CAMs, to
be expected, are a tad higher for south-southwestward facing
orography. As such. As noted in Day 1 ERO discussion, the soil
conditions are generally average, but the two day combination has
some potential for excessive rainfall/flooding with
mudslides/debris flows particularly near burn scars. As such, a
Marginal Risk of Excessive Rainfall was introduced, with
coordination from local forecast offices, for the central Oregon
coastal region.

While the strength of the moisture flux, wind flow resulting in
orographic ascent is much lower across the lower slopes of the
Oregon Cascade region, increased overall rainfall totals
throughout the 48hr period to 2-4", perhaps higher across numerous
large burn scars from the 2020 and 2021 seasons resulted in
expanding the Marginal Risk across to the lower slopes, below
freezing levels in the central Oregon Cascade Range.

Gallina


Day 3
Valid 12Z Mon Dec 20 2021 - 12Z Tue Dec 21 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Gallina


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!qPawITrikHMPHsW40W9u9JNFquA6dts9vKPw0wujtgF5= i1OJHSynDw39eLmts39x25qaHck8$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!qPawITrikHMPHsW40W9u9JNFquA6dts9vKPw0wujtgF5= i1OJHSynDw39eLmts39x25ypyxLf$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!qPawITrikHMPHsW40W9u9JNFquA6dts9vKPw0wujtgF5= i1OJHSynDw39eLmts39x2x1p8D2L$=20


$$




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FOUS30 KWBC 191538
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1037 AM EST Sun Dec 19 2021

Day 1
Valid 12Z Sun Dec 19 2021 - 12Z Mon Dec 20 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN WESTERN
OREGON...

16z update:
Recent observations along the central Oregon coastal range
indicate .25-.33"/hr rates. 12z Hi-Res CAMs continue to suggest an
additional 2-3" are possible across the Marginal Risk and HREF
probabilities continue to show similar rates peaking through 00z
before deep layer flow backs to reduce best favorable orientation.
As such, no substantive changes were made to the risk area.

Gallina


...Western Oregon...

Portions of western Oregon will be in the midst of a heavy
rainfall event at the beginning of the period, with southwesterly
onshore flow through much of the depth of the troposphere.
Important changes in the flow pattern will take place during the
forecast period as a trough digs sharply off the West Coast and
begins to close off a deep low around 38N/135W. The ribbon of
modest IVT (about 500 kg/m/s) will be in the process of weakening
around the start of the forecast period, before the flow backs (to
a more southerly direction) and increases once more in the
afternoon and evening hours (albeit mostly offshore). The end
result will be weaker flow that is less favorably positioned to
intercept the north-south mountain ranges in an orthogonal fashion
(thereby maximizing orographic lift on a larger scale).
Furthermore, other factors that could compensate somewhat for
weaker low-mid tropospheric winds, such as highly anomalous
atmospheric moisture or instability, are not really present
either. Indeed, 00Z HREF probabilities of even 0.5 inch per hour
rainfall rates are negligible for the entire forecast period.
Therefore, the threat of impactful heavy rain should be somewhat
localized -- where orographic ascent is more favorably maximized
with the wind shifts, or perhaps with some of the large burn scars
in the area. And with a threat of localized impacts, the Marginal
Risk across the area was maintained.

Lamers


Day 2
Valid 12Z Mon Dec 20 2021 - 12Z Tue Dec 21 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Lamers




Day 3
Valid 12Z Tue Dec 21 2021 - 12Z Wed Dec 22 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

...Southern Alabama, Southern Georgia, and the Florida Panhandle...
No risk area was outlined at the moment for Tuesday and Tuesday
Night along the Eastern Gulf Coast. Although heavy rain is in the
forecast, QPF is currently not particularly anomalous, and even
90th percentile PQPF values do not rise to even a 1-2 year average
annual recurrence interval. Nevertheless, there are signals for
somewhat anomalous available moisture (PWATs around the 90th
percentile for December), some instability (MUCAPE 200-500 j/kg),
and persistent forcing with a surface low forming in the eastern
Gulf and slowly shifting northeast. This could theoretically
support some localized heavy rain rates around or just over 1 inch
per hour in areas of persistent low-level convergence (that would
focus more organized convective clusters). This area will be
monitored for future outlooks, as there is still considerable
model spread even on basic facets of the scenario like placement
of the axis of heavy rain.

Lamers


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!s2LeGUAnkLXjWWbLvKbDyaRKW75HmaDqd0rFqqu8czCU= ge2CqQyYXTKBKNVY6GBhfGLSM9ij$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!s2LeGUAnkLXjWWbLvKbDyaRKW75HmaDqd0rFqqu8czCU= ge2CqQyYXTKBKNVY6GBhfBatLNwX$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!s2LeGUAnkLXjWWbLvKbDyaRKW75HmaDqd0rFqqu8czCU= ge2CqQyYXTKBKNVY6GBhfIBNBekr$=20


$$




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FOUS30 KWBC 191932
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
231 PM EST Sun Dec 19 2021

Day 1
Valid 16Z Sun Dec 19 2021 - 12Z Mon Dec 20 2021

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN WESTERN
OREGON...

16z update:
Recent observations along the central Oregon coastal range
indicate .25-.33"/hr rates. 12z Hi-Res CAMs continue to suggest an
additional 2-3" are possible across the Marginal Risk and HREF
probabilities continue to show similar rates peaking through 00z
before deep layer flow backs to reduce best favorable orientation.
As such, no substantive changes were made to the risk area.

Gallina


...Western Oregon...

Portions of western Oregon will be in the midst of a heavy
rainfall event at the beginning of the period, with southwesterly
onshore flow through much of the depth of the troposphere.
Important changes in the flow pattern will take place during the
forecast period as a trough digs sharply off the West Coast and
begins to close off a deep low around 38N/135W. The ribbon of
modest IVT (about 500 kg/m/s) will be in the process of weakening
around the start of the forecast period, before the flow backs (to
a more southerly direction) and increases once more in the
afternoon and evening hours (albeit mostly offshore). The end
result will be weaker flow that is less favorably positioned to
intercept the north-south mountain ranges in an orthogonal fashion
(thereby maximizing orographic lift on a larger scale).
Furthermore, other factors that could compensate somewhat for
weaker low-mid tropospheric winds, such as highly anomalous
atmospheric moisture or instability, are not really present
either. Indeed, 00Z HREF probabilities of even 0.5 inch per hour
rainfall rates are negligible for the entire forecast period.
Therefore, the threat of impactful heavy rain should be somewhat
localized -- where orographic ascent is more favorably maximized
with the wind shifts, or perhaps with some of the large burn scars
in the area. And with a threat of localized impacts, the Marginal
Risk across the area was maintained.

Lamers


Day 2
Valid 12Z Mon Dec 20 2021 - 12Z Tue Dec 21 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Gallina




Day 3
Valid 12Z Tue Dec 21 2021 - 12Z Wed Dec 22 2021

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

21z update:

...Southern Georgia, and the Florida Panhandle...
Global guidance continues to depict a very similar evolution with
respect to the surface cyclone and placement of potentially
excessive rainfall swath. Synoptically, the strong 1-2 standard
deviation shortwave, sharpens into the eastern Gulf reaching 90 to
95th percentiles for the time of year for negative anomalies.=20
This produces/maintains a strong low level cyclone that is
expected to have strong convection within deep layer moisture
convergence along the northern deformation zone of the cyclone.=20
Deep warm Gulf waters produce ample instability, but as the depth
reduces and reaches the shelf, rain-rates are expected to reduce
and be driven mainly by any retained weak to modest mid-level
instability along the down-shear deformation zone, which given
cell motions/cyclone track could provide a narrow corridor for
training and enhanced rainfall totals.=20

Unfortunately, the guidance continues to waver and be generally
inconsistent where the deformation axis aligns even at 48 to 72hrs
out. Generally, this could be as far north as AL/GA/FL border
intersection into central GA or as far south as the I-4 corridor,
with the average generally crossing across the Big Bend of Florida
north of the mouth of the Suwanee. This area and into the
Okefenokee Swamp generally has favorable soils to handle even
prolonged moderate rain rates and has been running about average
to slightly below average for precipitation and soil saturation,
so will maintain a less than 5 percent probability of FFG, until
guidance settles on a location or rainfall rates/totals increase.

Gallina


Prior Discussion
~~~~~~~~~~~~~~~~~~
No risk area was outlined at the moment for Tuesday and Tuesday
Night along the Eastern Gulf Coast. Although heavy rain is in the
forecast, QPF is currently not particularly anomalous, and even
90th percentile PQPF values do not rise to even a 1-2 year average
annual recurrence interval. Nevertheless, there are signals for
somewhat anomalous available moisture (PWATs around the 90th
percentile for December), some instability (MUCAPE 200-500 j/kg),
and persistent forcing with a surface low forming in the eastern
Gulf and slowly shifting northeast. This could theoretically
support some localized heavy rain rates around or just over 1 inch
per hour in areas of persistent low-level convergence (that would
focus more organized convective clusters). This area will be
monitored for future outlooks, as there is still considerable
model spread even on basic facets of the scenario like placement
of the axis of heavy rain.

Lamers


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!rz1TPwX9lrCtr3VFVLYFa86klWoyVg_Dk6TmH72kSmYJ= rROQwjbfjZuXcTWz4yCVWMD4DPeF$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!rz1TPwX9lrCtr3VFVLYFa86klWoyVg_Dk6TmH72kSmYJ= rROQwjbfjZuXcTWz4yCVWETGeRLR$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!rz1TPwX9lrCtr3VFVLYFa86klWoyVg_Dk6TmH72kSmYJ= rROQwjbfjZuXcTWz4yCVWMmilXUH$=20


$$




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FOUS30 KWBC 280752
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
252 AM EST Tue Dec 28 2021

Day 1
Valid 12Z Tue Dec 28 2021 - 12Z Wed Dec 29 2021

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
THE MIDWEST AND SOUTHWEST PA/NORTHERN WV...

...Mid-Mississippi/Ohio Valleys into Southwest PA...
A tightly packed deep mid to upper level southwesterly to
northeasterly flow regime sets up a solid frontal zone across the
area of concern between a very deep cold low in Manitoba and an
unseasonably strong/warm sub-tropical ridge over the Bahamas
extending into the Gulf of Mexico. A small compact shortwave will
rounding the base of the positive trof over the Southwest into the
Central Plains by the start of the forecast period, 28.12z,
spurring a fast moving surface wave into the Mid-Mississippi
Valley. Strong WAA (35-50kts at 850mb) ahead of the wave will
allow for upglide across the boundary intersecting a modest pool
of 250-500 J/kg of MUCAPE is supported by above normal theta-E and
with 2-3 standard deviations of moisture available in the warm
sector with TPW values between 1-1.25". It is the initial
strength of the moisture flux across the boundary likely to have
ongoing convection starting across the MOKSAROK. Deep layered
steering flow just above the strong WAA moist convergence layer
(~85H) is quite unidirectional through depth to support a line of
convection and potential training environment. Hourly rates of
1-1.5"/hr supporting 1.5-2.5" totals in less than 3hrs.

Currently, Hi-Res CAMs are suggestive of the axis of training to
be a county or two north and west of the more hydrologically
sensitive swath of enhanced saturated soil conditions from the NW
AR Ozark Plateau to Perryville, MO to between Terre
Haute/Vincennes IND. Here, NASA LIS 0-40cm saturation ratios are
finally starting to come down to normal but remain about 70& in MO
and 40-60% into central IND; as AHPS 2-week anomalies are still
200-300% of normal to 150-200%, respectively. Any deviation
southward initially could provoke an enhanced risk, but at this
time, guidance is solidly supported to remain north enough to
maintain a Marginal Risk of Excessive Rainfall at this time.

Toward the afternoon/evening hours, the triggering shortwave will
be rapidly weakening into confluent mid-level flow and the surface
wave will shear into the frontal boundary across the Ohio Valley,
weakening any ongoing mid-level convection. Still, the strength
of the flux and persistence in the vicinity of the boundary with
this anomalous flow could maintain modest showers and totals that
may be in reach of the lowered FFGs. This is the case across the
Upper Wabash Basin and into the upslope region of the Allegheny
Plateau of southwest PA, northern WV. There is likely to be a
lull in excessive threat across E Ohio, so the question is whether
to connect up or draw this as a separate area, and given the risk
is driven mainly by HREF probability of 1"/6hr up to 20-30%
intersecting with similar FFG values (<1"/6hr) have decided to go
with the smaller separated Marginal Risk area in southwest
PA/northern WV.


...Kentucky...
There are a few guidance members that suggest reinvigoration of
overrunning, training convective elements across Central KY into
the northern Cumberland Plateau, mainly the ARWs and the ECMWF.=20
MUCAPEs of 150-300 J/kg are forecast and moisture/flux remains
highly anomalous, but rain rates are not expected to be over 1"
and the area has been recently well below average per AHPS and
0-40cm soil saturation show 10-20% normal values, so believe
flooding threat will be below 5% coverage and so is not depicted
in a categorized area at this time.


...Central Gulf through Southern Appalachians/southern Cumberland
Plateau...
The aforementioned compact mid-level shortwave approach is suffice
to break down ridging across the Gulf, allowing for sfc-85H bubble
of increased moisture and instability to stream northward along
the confluent northwesterly edge of the slowly retreating ridge.=20
Increasing instability at the Gulf/LA coast with values of
1000-1500 J/kg and confluent streamer bands may be sufficient to
support some shallow inconsistent thunderstorm development
throughout the morning and have some potential for training from
the Central Gulf Coast. As the day progresses this sub-tropical
shortwave/slug of moisture will stream north-northeast to
northeast into the southern Appalachians/Cumberland Plateau of
AL/TN/NW GA, enhancing TPW values to 1.5-1.7" and MUCAPE up to
1000 J/kg after 00z. Tightening low level confluent flow may
producing increased convergence for enhanced thunderstorms with
potential of 1.5-1.75"/hr rates. However, there is very high
inconsistency in placement east to west and strength of the
convergence within the guidance suite. The 00z HRRR was most
aggressive, further east with training across the Southern
Appalachians in SE TN/N GA to support a Marginal Risk; though ARW
solutions are delayed, later into the Day 2 period or further west
as suggested by the NAM-Conest/FV3CAM. Higher FFG, dry ground
conditions further support not delineating a categorized risk area
at this time, though it will be going into the Day 2 period (after 29.12z).=20=20=20

Gallina


Day 2

The Day 2 outlook will be updated by 0830Z.


Day 3

The Day 3 outlook will be updated by 0830Z.


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!p1qWBcy-TxXVQRZsJvT3SbSxWmU2Sb006eDjOMitFug-= KIF-Ukgx9d_1GwnkXgmUIghnLWOV$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!p1qWBcy-TxXVQRZsJvT3SbSxWmU2Sb006eDjOMitFug-= KIF-Ukgx9d_1GwnkXgmUIjswOPcG$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!p1qWBcy-TxXVQRZsJvT3SbSxWmU2Sb006eDjOMitFug-= KIF-Ukgx9d_1GwnkXgmUIn-8D66W$=20


$$




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FOUS30 KWBC 280753
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
252 AM EST Tue Dec 28 2021

Day 1
Valid 12Z Tue Dec 28 2021 - 12Z Wed Dec 29 2021

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
THE MIDWEST AND SOUTHWEST PA/NORTHERN WV...

...Mid-Mississippi/Ohio Valleys into Southwest PA...
A tightly packed deep mid to upper level southwesterly to
northeasterly flow regime sets up a solid frontal zone across the
area of concern between a very deep cold low in Manitoba and an
unseasonably strong/warm sub-tropical ridge over the Bahamas
extending into the Gulf of Mexico. A small compact shortwave will
rounding the base of the positive trof over the Southwest into the
Central Plains by the start of the forecast period, 28.12z,
spurring a fast moving surface wave into the Mid-Mississippi
Valley. Strong WAA (35-50kts at 850mb) ahead of the wave will
allow for upglide across the boundary intersecting a modest pool
of 250-500 J/kg of MUCAPE is supported by above normal theta-E and
with 2-3 standard deviations of moisture available in the warm
sector with TPW values between 1-1.25". It is the initial
strength of the moisture flux across the boundary likely to have
ongoing convection starting across the MOKSAROK. Deep layered
steering flow just above the strong WAA moist convergence layer
(~85H) is quite unidirectional through depth to support a line of
convection and potential training environment. Hourly rates of
1-1.5"/hr supporting 1.5-2.5" totals in less than 3hrs.

Currently, Hi-Res CAMs are suggestive of the axis of training to
be a county or two north and west of the more hydrologically
sensitive swath of enhanced saturated soil conditions from the NW
AR Ozark Plateau to Perryville, MO to between Terre
Haute/Vincennes IND. Here, NASA LIS 0-40cm saturation ratios are
finally starting to come down to normal but remain about 70& in MO
and 40-60% into central IND; as AHPS 2-week anomalies are still
200-300% of normal to 150-200%, respectively. Any deviation
southward initially could provoke an enhanced risk, but at this
time, guidance is solidly supported to remain north enough to
maintain a Marginal Risk of Excessive Rainfall at this time.

Toward the afternoon/evening hours, the triggering shortwave will
be rapidly weakening into confluent mid-level flow and the surface
wave will shear into the frontal boundary across the Ohio Valley,
weakening any ongoing mid-level convection. Still, the strength
of the flux and persistence in the vicinity of the boundary with
this anomalous flow could maintain modest showers and totals that
may be in reach of the lowered FFGs. This is the case across the
Upper Wabash Basin and into the upslope region of the Allegheny
Plateau of southwest PA, northern WV. There is likely to be a
lull in excessive threat across E Ohio, so the question is whether
to connect up or draw this as a separate area, and given the risk
is driven mainly by HREF probability of 1"/6hr up to 20-30%
intersecting with similar FFG values (<1"/6hr) have decided to go
with the smaller separated Marginal Risk area in southwest
PA/northern WV.


...Kentucky...
There are a few guidance members that suggest reinvigoration of
overrunning, training convective elements across Central KY into
the northern Cumberland Plateau, mainly the ARWs and the ECMWF.=20
MUCAPEs of 150-300 J/kg are forecast and moisture/flux remains
highly anomalous, but rain rates are not expected to be over 1"
and the area has been recently well below average per AHPS and
0-40cm soil saturation show 10-20% normal values, so believe
flooding threat will be below 5% coverage and so is not depicted
in a categorized area at this time.


...Central Gulf through Southern Appalachians/southern Cumberland
Plateau...
The aforementioned compact mid-level shortwave approach is suffice
to break down ridging across the Gulf, allowing for sfc-85H bubble
of increased moisture and instability to stream northward along
the confluent northwesterly edge of the slowly retreating ridge.=20
Increasing instability at the Gulf/LA coast with values of
1000-1500 J/kg and confluent streamer bands may be sufficient to
support some shallow inconsistent thunderstorm development
throughout the morning and have some potential for training from
the Central Gulf Coast. As the day progresses this sub-tropical
shortwave/slug of moisture will stream north-northeast to
northeast into the southern Appalachians/Cumberland Plateau of
AL/TN/NW GA, enhancing TPW values to 1.5-1.7" and MUCAPE up to
1000 J/kg after 00z. Tightening low level confluent flow may
producing increased convergence for enhanced thunderstorms with
potential of 1.5-1.75"/hr rates. However, there is very high
inconsistency in placement east to west and strength of the
convergence within the guidance suite. The 00z HRRR was most
aggressive, further east with training across the Southern
Appalachians in SE TN/N GA to support a Marginal Risk; though ARW
solutions are delayed, later into the Day 2 period or further west
as suggested by the NAM-Conest/FV3CAM. Higher FFG, dry ground
conditions further support not delineating a categorized risk area
at this time, though it will be going into the Day 2 period (after 29.12z).=20=20=20

Gallina


Day 2
Valid 12Z Tue Dec 28 2021 - 12Z Wed Dec 29 2021

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE
TENNESSEE VALLEY/SOUTHERN APPALACHIANS AND SOUTHERN CALIFORNIA...

...Tennessee Valley to Central Appalachians...
At the start of the forecast period, 29.12z, the initial shortwave
has sheared into the confluent southwesterly flow across the
eastern Great Lakes leaving a quasi-stationary front across the
Central Appalachians and Kentucky with inflection toward the Ozark
Plateau, at the intersection of the warm, moist airmass emanating
from the Gulf of Mexico. Ongoing convective cells Meanwhile, the
next shortwave to round the base of the large scale trof across
the West, will once again strengthen southwesterly flow helping to
draw mid-level subtropical Pacific moisture across the lower MS
valley, adding to the low-level returning Gulf Moisture. TPWs
will be increased to 1.5-1.7" across the Delta region while and
instability will be steadily increasing with CAPEs to 1500 J/kg
into central MS, while a more modest but sufficient 500-750 J/kg
should reach into the Tennessee Valley, where the returning warm
front will help to trigger moisture convergence and deeper
thunderstorm development. While there is a good probability for
stronger severe rotating storms southward into MS/AL, enhancing
mesoscale moisture flux for increased rainfall efficiency; it is
along the warm front where multiple cells have the potential to
train given the length of moisture flux convergence downstream and
parallel to the boundary. Rates of 1.5" are possible and given
training 6hr probabilities of exceeding 3" are as high as 35%
across central TN by 00z. While instability will reduce and
likewise with the rainfall intensity. increased deep-layer
confluence further east across the Cumberland Plateau should help
to expand the complex to produce broad 2-3" totals and potential
in short duration as depicted by the NAM-Nest, GFS/NAM, ECMWF,
ICON and Gem-Regional. As such, the potential for flash flooding
is about the same as the FFG values reduce to the east with lower
threshold of 1-1.5"/hr & 1.5-2"/3hrs across the Plateau into the
Central Appalachian Mountains producing possibility of exceedance.
As such, a Slight Risk of Excessive Rainfall has been added from
the NE corner of MS across TN/N AL into far SE KY. A Marginal Risk
extends southward across central MS, AL into GA where some of the
stronger cells could produce isolated rain-rates capable of
short-term FFG exceedance.


...Southern California...
An upper-level shortwave will be starting to amplify along the
southwester portion of the larger scale synoptic trof dominating
Canada into the Northern Rockies. A wave further north in the
stream will undercut across the Northern Rockies and allow for the
shortwave to buckle further as it reaches the California Bight
about 30.06z. As is typical with waves at the periphery of strong
northern stream flow, there remains significant timing differences
in the guidance resulting in large but reducing spread west to
east, but the depth in latitude seems to be coming to strong
agreement. It is the placement of the wave as it closes off
across the Catalina Islands that will allow for the surface flow
to back, tighten low level moisture gradients with solid speed and
directional divergence aloft, weak CAA will also steepen lapse
rates for 100-200 J/kg even onshore across Los Angeles and Orange
counties for some shallow convective cells to develop. SoCal's
proximity to the mean mid-level 5H pinching point will also
support weakened cell motions to allow for cells to propagate
along self-generated cold pools and hang up along/near terrain
while maintaining favorable moisture flux. With the positives of
the dynamics, the limiting factor will be the moisture which is
likely to be limited to .75 to 1" limiting rainfall efficiency and
overall totals. However, recent well above normal rainfall across
the region (500-600% of normal per AHPS 7-day anomalies), deep
soil saturation to 80-90% per NASA SPoRT LIS 0-40 ratios along
with urban environment suggests rates of .5-1"/hr and localized
totals up to 2" across the valley floor may contribute to flash
flooding.=20

Low-level flow is likely to be 20-30kts into the transverse range,
veering toward the Peninsular range toward the end of the forecast
period. Freezing levels may start low AoA 5000ft but should
slowly increasing with the WAA, perhaps allowing for all rain
across the southern most peaks in San Diego county. It is within
orographic ascent regions that will provide longer
duration/moderate rainfall adding to the saturated areas as well
with an additional 2-4". As such, a Slight Risk of Excessive
Rainfall was introduced to greatest model placement agreement
though may need to be expanded south and eastward given timing
trends.

Gallina

Day 3

The Day 3 outlook will be updated by 0830Z.


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!rMr1mb8GdZGoLIvrfMsaDVTWZPJtBnItF4ykZ-J8llH8= VLDi_BRgIBcJLpOIzcroMD_Sv__v$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!rMr1mb8GdZGoLIvrfMsaDVTWZPJtBnItF4ykZ-J8llH8= VLDi_BRgIBcJLpOIzcroMHn4XcYF$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!rMr1mb8GdZGoLIvrfMsaDVTWZPJtBnItF4ykZ-J8llH8= VLDi_BRgIBcJLpOIzcroMCakHt6y$=20


$$




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FOUS30 KWBC 280753
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
253 AM EST Tue Dec 28 2021

Day 1
Valid 12Z Tue Dec 28 2021 - 12Z Wed Dec 29 2021

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
THE MIDWEST AND SOUTHWEST PA/NORTHERN WV...

...Mid-Mississippi/Ohio Valleys into Southwest PA...
A tightly packed deep mid to upper level southwesterly to
northeasterly flow regime sets up a solid frontal zone across the
area of concern between a very deep cold low in Manitoba and an
unseasonably strong/warm sub-tropical ridge over the Bahamas
extending into the Gulf of Mexico. A small compact shortwave will
rounding the base of the positive trof over the Southwest into the
Central Plains by the start of the forecast period, 28.12z,
spurring a fast moving surface wave into the Mid-Mississippi
Valley. Strong WAA (35-50kts at 850mb) ahead of the wave will
allow for upglide across the boundary intersecting a modest pool
of 250-500 J/kg of MUCAPE is supported by above normal theta-E and
with 2-3 standard deviations of moisture available in the warm
sector with TPW values between 1-1.25". It is the initial
strength of the moisture flux across the boundary likely to have
ongoing convection starting across the MOKSAROK. Deep layered
steering flow just above the strong WAA moist convergence layer
(~85H) is quite unidirectional through depth to support a line of
convection and potential training environment. Hourly rates of
1-1.5"/hr supporting 1.5-2.5" totals in less than 3hrs.

Currently, Hi-Res CAMs are suggestive of the axis of training to
be a county or two north and west of the more hydrologically
sensitive swath of enhanced saturated soil conditions from the NW
AR Ozark Plateau to Perryville, MO to between Terre
Haute/Vincennes IND. Here, NASA LIS 0-40cm saturation ratios are
finally starting to come down to normal but remain about 70& in MO
and 40-60% into central IND; as AHPS 2-week anomalies are still
200-300% of normal to 150-200%, respectively. Any deviation
southward initially could provoke an enhanced risk, but at this
time, guidance is solidly supported to remain north enough to
maintain a Marginal Risk of Excessive Rainfall at this time.

Toward the afternoon/evening hours, the triggering shortwave will
be rapidly weakening into confluent mid-level flow and the surface
wave will shear into the frontal boundary across the Ohio Valley,
weakening any ongoing mid-level convection. Still, the strength
of the flux and persistence in the vicinity of the boundary with
this anomalous flow could maintain modest showers and totals that
may be in reach of the lowered FFGs. This is the case across the
Upper Wabash Basin and into the upslope region of the Allegheny
Plateau of southwest PA, northern WV. There is likely to be a
lull in excessive threat across E Ohio, so the question is whether
to connect up or draw this as a separate area, and given the risk
is driven mainly by HREF probability of 1"/6hr up to 20-30%
intersecting with similar FFG values (<1"/6hr) have decided to go
with the smaller separated Marginal Risk area in southwest
PA/northern WV.


...Kentucky...
There are a few guidance members that suggest reinvigoration of
overrunning, training convective elements across Central KY into
the northern Cumberland Plateau, mainly the ARWs and the ECMWF.=20
MUCAPEs of 150-300 J/kg are forecast and moisture/flux remains
highly anomalous, but rain rates are not expected to be over 1"
and the area has been recently well below average per AHPS and
0-40cm soil saturation show 10-20% normal values, so believe
flooding threat will be below 5% coverage and so is not depicted
in a categorized area at this time.


...Central Gulf through Southern Appalachians/southern Cumberland
Plateau...
The aforementioned compact mid-level shortwave approach is suffice
to break down ridging across the Gulf, allowing for sfc-85H bubble
of increased moisture and instability to stream northward along
the confluent northwesterly edge of the slowly retreating ridge.=20
Increasing instability at the Gulf/LA coast with values of
1000-1500 J/kg and confluent streamer bands may be sufficient to
support some shallow inconsistent thunderstorm development
throughout the morning and have some potential for training from
the Central Gulf Coast. As the day progresses this sub-tropical
shortwave/slug of moisture will stream north-northeast to
northeast into the southern Appalachians/Cumberland Plateau of
AL/TN/NW GA, enhancing TPW values to 1.5-1.7" and MUCAPE up to
1000 J/kg after 00z. Tightening low level confluent flow may
producing increased convergence for enhanced thunderstorms with
potential of 1.5-1.75"/hr rates. However, there is very high
inconsistency in placement east to west and strength of the
convergence within the guidance suite. The 00z HRRR was most
aggressive, further east with training across the Southern
Appalachians in SE TN/N GA to support a Marginal Risk; though ARW
solutions are delayed, later into the Day 2 period or further west
as suggested by the NAM-Conest/FV3CAM. Higher FFG, dry ground
conditions further support not delineating a categorized risk area
at this time, though it will be going into the Day 2 period (after 29.12z).=20=20=20

Gallina


Day 2
Valid 12Z Wed Dec 29 2021 - 12Z Thu Dec 30 2021

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE
TENNESSEE VALLEY/SOUTHERN APPALACHIANS AND SOUTHERN CALIFORNIA...

...Tennessee Valley to Central Appalachians...
At the start of the forecast period, 29.12z, the initial shortwave
has sheared into the confluent southwesterly flow across the
eastern Great Lakes leaving a quasi-stationary front across the
Central Appalachians and Kentucky with inflection toward the Ozark
Plateau, at the intersection of the warm, moist airmass emanating
from the Gulf of Mexico. Ongoing convective cells Meanwhile, the
next shortwave to round the base of the large scale trof across
the West, will once again strengthen southwesterly flow helping to
draw mid-level subtropical Pacific moisture across the lower MS
valley, adding to the low-level returning Gulf Moisture. TPWs
will be increased to 1.5-1.7" across the Delta region while and
instability will be steadily increasing with CAPEs to 1500 J/kg
into central MS, while a more modest but sufficient 500-750 J/kg
should reach into the Tennessee Valley, where the returning warm
front will help to trigger moisture convergence and deeper
thunderstorm development. While there is a good probability for
stronger severe rotating storms southward into MS/AL, enhancing
mesoscale moisture flux for increased rainfall efficiency; it is
along the warm front where multiple cells have the potential to
train given the length of moisture flux convergence downstream and
parallel to the boundary. Rates of 1.5" are possible and given
training 6hr probabilities of exceeding 3" are as high as 35%
across central TN by 00z. While instability will reduce and
likewise with the rainfall intensity. increased deep-layer
confluence further east across the Cumberland Plateau should help
to expand the complex to produce broad 2-3" totals and potential
in short duration as depicted by the NAM-Nest, GFS/NAM, ECMWF,
ICON and Gem-Regional. As such, the potential for flash flooding
is about the same as the FFG values reduce to the east with lower
threshold of 1-1.5"/hr & 1.5-2"/3hrs across the Plateau into the
Central Appalachian Mountains producing possibility of exceedance.
As such, a Slight Risk of Excessive Rainfall has been added from
the NE corner of MS across TN/N AL into far SE KY. A Marginal Risk
extends southward across central MS, AL into GA where some of the
stronger cells could produce isolated rain-rates capable of
short-term FFG exceedance.


...Southern California...
An upper-level shortwave will be starting to amplify along the
southwester portion of the larger scale synoptic trof dominating
Canada into the Northern Rockies. A wave further north in the
stream will undercut across the Northern Rockies and allow for the
shortwave to buckle further as it reaches the California Bight
about 30.06z. As is typical with waves at the periphery of strong
northern stream flow, there remains significant timing differences
in the guidance resulting in large but reducing spread west to
east, but the depth in latitude seems to be coming to strong
agreement. It is the placement of the wave as it closes off
across the Catalina Islands that will allow for the surface flow
to back, tighten low level moisture gradients with solid speed and
directional divergence aloft, weak CAA will also steepen lapse
rates for 100-200 J/kg even onshore across Los Angeles and Orange
counties for some shallow convective cells to develop. SoCal's
proximity to the mean mid-level 5H pinching point will also
support weakened cell motions to allow for cells to propagate
along self-generated cold pools and hang up along/near terrain
while maintaining favorable moisture flux. With the positives of
the dynamics, the limiting factor will be the moisture which is
likely to be limited to .75 to 1" limiting rainfall efficiency and
overall totals. However, recent well above normal rainfall across
the region (500-600% of normal per AHPS 7-day anomalies), deep
soil saturation to 80-90% per NASA SPoRT LIS 0-40 ratios along
with urban environment suggests rates of .5-1"/hr and localized
totals up to 2" across the valley floor may contribute to flash
flooding.=20

Low-level flow is likely to be 20-30kts into the transverse range,
veering toward the Peninsular range toward the end of the forecast
period. Freezing levels may start low AoA 5000ft but should
slowly increasing with the WAA, perhaps allowing for all rain
across the southern most peaks in San Diego county. It is within
orographic ascent regions that will provide longer
duration/moderate rainfall adding to the saturated areas as well
with an additional 2-4". As such, a Slight Risk of Excessive
Rainfall was introduced to greatest model placement agreement
though may need to be expanded south and eastward given timing
trends.

Gallina

Day 3
Valid 12Z Wed Dec 29 2021 - 12Z Thu Dec 30 2021

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
SOUTHERN CALIFORNIA...

...Southern California...
By the start of the day 3 period, 30.12z, the closed low will have
dropped fully into the California Bight while the low level flow
will start to direct more into far southern California into the
Peninsular Ranges. However, while improving, much like Day 2,
there is timing spread on that frontal zone/moisture plume enough
to keep a Marginal Risk of Excessive Rainfall for an additional
1-2" perhaps higher in highest slopes of the southwest facing
terrain from LA county southward across San Diego County. While
becoming less likely with slightly faster trend in the 00z
guidance, there does still remain a potential for an upgrade to a
Slight Risk with subsequent guidance cycles; especially if trend
shifts back toward slower solutions with Hi-Res CAMs.=20

Gallina


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!oLLWRsiQLdmMR3ahd7DsiMtsaP7GN6ReRDvuyyiUcGcI= 5uuk2R82afWGvRENdwohJII87cE7$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!oLLWRsiQLdmMR3ahd7DsiMtsaP7GN6ReRDvuyyiUcGcI= 5uuk2R82afWGvRENdwohJP6RZe4s$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!oLLWRsiQLdmMR3ahd7DsiMtsaP7GN6ReRDvuyyiUcGcI= 5uuk2R82afWGvRENdwohJBmzvrkE$=20


$$




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FOUS30 KWBC 290746
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
245 AM EST Wed Dec 29 2021

Day 1
Valid 12Z Wed Dec 29 2021 - 12Z Thu Dec 30 2021

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE
TENNESSEE VALLEY/SOUTHERN APPALACHIANS AND SOUTHERN CALIFORNIA...

...Tennessee Valley to Central Appalachians...

At the start of the day 1 period, the quasi-stationary front will
continue to sag southward across central and eastern Kentucky and
through the Central Appalachians. Further south, there is a good
possibility there will be ongoing but weakening scattered
convection along the northwest periphery of the synoptic-scale
subtropical ridge in the Bahamas and the impinging aforementioned
northern stream flow across the southern Cumberland Plateau,
southern Appalachians. These cells help to demarcate a ribbon of
enhanced sub-tropical moisture/higher theta-E air originating from
the Western Caribbean, but solidly in place across the Lower
Mississippi River Valley. The next in a series of shortwaves will
be emerging into the south-central Plains and rocketing northeast
through the strong southwest to northeast flow. This wave and
associated buckle in the 3H jet will provide strong synoptic
dynamics within the right entrance region to develop a new surface
wave along the front through the Ozark Plateau into the Tri-Rivers
confluence region and through the Ohio Valley by late day.

Strong moisture flux in the 8-5H layer from the sub-tropic stream
will over-top the return moisture from the Gulf and increase total
PWAT values to 1.5-1.7" across the MS Delta Region into the
Tennessee Valley. Combined with growing unstable environment with
CAPEs of 1500 J/kg into central MS and 750-1000 J/kg into W TN and
the strengthening forcing, strong thunderstorms are expected with
high rainfall rates of 1.5-2"/hr. Strong moisture flux
convergence along/south of the returning front across W TN/N MS
will have increased length to support multiple cells and with deep
layered unidirectional flow, promoting potential for training.=20
Likely due to confluent moisture streams, Hi-Res CAMs are
bifurcating on location of best training/convergence resulting in
lowered HREF Probability values, but guidance does support the
evolution with a slight southward trend, particularly in the
global guidance members. As such, the Slight Risk has been
expanded west and south, centering on area that received 1-2" of
rainfall overnight early Wednesday across N AL. By late evening,
deep layer flow will support multiple rounds across E TN, though
likely to be weaker, in general, due to proximity from the
instability source further upstream. Yet, confidence is higher
across this area for the Slight Risk as HREF probabilities exceed
70% for higher rates/3hr totals.

South across the lower MS River Valley, individual cells may have
a greater potential for cell rotation (see SPC D1 discussion) and
that will support enhanced storm-scale moisture flux convergence
to enhance moisture flux and rainfall efficiency. However, given
orientation to the flow and potential for greater right-hand
turning across the mean deep layer flow should be much less likely
for training across central and southern MS and progressing into
AL through the evening, resulting in a more scattered nature to
flash flooding potential and as such, are encompassed in a broader
Marginal Risk southward.


...Southern California...
An upper-level shortwave will be starting to amplify along the
central California coast throughout the day before swinging more
positive to neutral tilt while starting to pinch off into a closed
low by 30.12z near Point Conception. Models continue show an
increase in spread due to timing and how strong it closes off the
low with the NAM/UKMET a bit slower/deeper and southward relative
the remaining suite and results in a fairly sizable timing
difference with the approach of the cold front/moisture plume.=20=20
Still, all solutions do depict strengthening and backing flow to
support enhanced moisture convergence with 30-40kts of 85H flow
directed toward both the Transverse and Peninsular Ranges with
time. Steepening lapse rates due to the approach of the cold
upper low aloft may further support and areal expansion of weak
instability to 250 J/kg within moderately diffluent flow aloft
supporting increased vertical depth to showers/thunderstorms
resulting in enhanced rain rates of up to .5"/hr even in the lower
elevations. Slow trending upward with moisture to 1" and IVT
values ticking up to 400 to 500 kg/ms further provide confidence
to heavy rainfall signatures even across areas without orographic
enhancement with 1-2" possible.=20

Favorably directed low to mid-level flow will support enhanced
orographic ascent across the Transverse Range while also
supporting WAA to raise snow levels throughout the forecast
period. While the highest peaks of the San Gabriel and San
Bernardino Ranges will continue to have heavy snow, mid-slope
rainfall totals of 2-4+", perhaps over some snow melt and
saturated soils due to 500-600% of normal rainfall over the last
week (per AHPS), mud slide, debris flows and flash flooding are
possible supporting the Slight Risk already in place. Hi-Res
CAM's finer resolution helps to refine the Slight Risk area a bit
more to expand across the Santa Monica Range, Santa Ana, Palomar
mountains as well as mid-slopes of the San Bernadino Range. Slow
NAM/NAM-Nest solutions while of lower probability keep the
westward extent of the Marginal across Santa Barbara county at
this time.=20

Gallina


Day 2

The Day 2 outlook will be updated by 0830Z.


Day 3

The Day 3 outlook will be updated by 0830Z.


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!qRgeyDRlHNG4s-c8azSRu9eEuQmcGZw9Xr6ZlchgucKv= p_tr_h_4bxWubOSD4UxOqm-waPmy$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!qRgeyDRlHNG4s-c8azSRu9eEuQmcGZw9Xr6ZlchgucKv= p_tr_h_4bxWubOSD4UxOql4MAcoP$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!qRgeyDRlHNG4s-c8azSRu9eEuQmcGZw9Xr6ZlchgucKv= p_tr_h_4bxWubOSD4UxOqpA8LV9_$=20


$$




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FOUS30 KWBC 290747
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
246 AM EST Wed Dec 29 2021

Day 1
Valid 12Z Wed Dec 29 2021 - 12Z Thu Dec 30 2021

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE
TENNESSEE VALLEY/SOUTHERN APPALACHIANS AND SOUTHERN CALIFORNIA...

...Tennessee Valley to Central Appalachians...

At the start of the day 1 period, the quasi-stationary front will
continue to sag southward across central and eastern Kentucky and
through the Central Appalachians. Further south, there is a good
possibility there will be ongoing but weakening scattered
convection along the northwest periphery of the synoptic-scale
subtropical ridge in the Bahamas and the impinging aforementioned
northern stream flow across the southern Cumberland Plateau,
southern Appalachians. These cells help to demarcate a ribbon of
enhanced sub-tropical moisture/higher theta-E air originating from
the Western Caribbean, but solidly in place across the Lower
Mississippi River Valley. The next in a series of shortwaves will
be emerging into the south-central Plains and rocketing northeast
through the strong southwest to northeast flow. This wave and
associated buckle in the 3H jet will provide strong synoptic
dynamics within the right entrance region to develop a new surface
wave along the front through the Ozark Plateau into the Tri-Rivers
confluence region and through the Ohio Valley by late day.

Strong moisture flux in the 8-5H layer from the sub-tropic stream
will over-top the return moisture from the Gulf and increase total
PWAT values to 1.5-1.7" across the MS Delta Region into the
Tennessee Valley. Combined with growing unstable environment with
CAPEs of 1500 J/kg into central MS and 750-1000 J/kg into W TN and
the strengthening forcing, strong thunderstorms are expected with
high rainfall rates of 1.5-2"/hr. Strong moisture flux
convergence along/south of the returning front across W TN/N MS
will have increased length to support multiple cells and with deep
layered unidirectional flow, promoting potential for training.=20
Likely due to confluent moisture streams, Hi-Res CAMs are
bifurcating on location of best training/convergence resulting in
lowered HREF Probability values, but guidance does support the
evolution with a slight southward trend, particularly in the
global guidance members. As such, the Slight Risk has been
expanded west and south, centering on area that received 1-2" of
rainfall overnight early Wednesday across N AL. By late evening,
deep layer flow will support multiple rounds across E TN, though
likely to be weaker, in general, due to proximity from the
instability source further upstream. Yet, confidence is higher
across this area for the Slight Risk as HREF probabilities exceed
70% for higher rates/3hr totals.

South across the lower MS River Valley, individual cells may have
a greater potential for cell rotation (see SPC D1 discussion) and
that will support enhanced storm-scale moisture flux convergence
to enhance moisture flux and rainfall efficiency. However, given
orientation to the flow and potential for greater right-hand
turning across the mean deep layer flow should be much less likely
for training across central and southern MS and progressing into
AL through the evening, resulting in a more scattered nature to
flash flooding potential and as such, are encompassed in a broader
Marginal Risk southward.


...Southern California...
An upper-level shortwave will be starting to amplify along the
central California coast throughout the day before swinging more
positive to neutral tilt while starting to pinch off into a closed
low by 30.12z near Point Conception. Models continue show an
increase in spread due to timing and how strong it closes off the
low with the NAM/UKMET a bit slower/deeper and southward relative
the remaining suite and results in a fairly sizable timing
difference with the approach of the cold front/moisture plume.=20=20
Still, all solutions do depict strengthening and backing flow to
support enhanced moisture convergence with 30-40kts of 85H flow
directed toward both the Transverse and Peninsular Ranges with
time. Steepening lapse rates due to the approach of the cold
upper low aloft may further support and areal expansion of weak
instability to 250 J/kg within moderately diffluent flow aloft
supporting increased vertical depth to showers/thunderstorms
resulting in enhanced rain rates of up to .5"/hr even in the lower
elevations. Slow trending upward with moisture to 1" and IVT
values ticking up to 400 to 500 kg/ms further provide confidence
to heavy rainfall signatures even across areas without orographic
enhancement with 1-2" possible.=20

Favorably directed low to mid-level flow will support enhanced
orographic ascent across the Transverse Range while also
supporting WAA to raise snow levels throughout the forecast
period. While the highest peaks of the San Gabriel and San
Bernardino Ranges will continue to have heavy snow, mid-slope
rainfall totals of 2-4+", perhaps over some snow melt and
saturated soils due to 500-600% of normal rainfall over the last
week (per AHPS), mud slide, debris flows and flash flooding are
possible supporting the Slight Risk already in place. Hi-Res
CAM's finer resolution helps to refine the Slight Risk area a bit
more to expand across the Santa Monica Range, Santa Ana, Palomar
mountains as well as mid-slopes of the San Bernadino Range. Slow
NAM/NAM-Nest solutions while of lower probability keep the
westward extent of the Marginal across Santa Barbara county at
this time.=20

Gallina


Day 2
Valid 12Z Wed Dec 29 2021 - 12Z Thu Dec 30 2021

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
SOUTHERN CALIFORNIA...

...Southern California...
By the start of the day 2 period, 30/12z, the shortwave will have
become closed off entering the California Bight. The associated
surface low will move south-southeast through the Channel Islands
and with the 85H low still in proximity, low-level flow and
moisture transport will continue to be directed into southern
California into Day 2. The Hi-Res CAMs along with NAM/NAM-Nest
solutions continue to remain relatively slow mainly due to
stronger that average closed low solutions that delay eastward
progression of the moisture feed/transport. Large scale pattern
suggests next kicker wave upstream is likely to keep the shortwave
progressive and kicking through northern Baja California by early
Friday and the NAM/UKMET are just outlier solutions to this
evolution for overall preference.

With that stated, overall stronger surface wave and therefore
moisture flux transport within the 1" Total PWat narrow plume has
trended slower and allows for longer duration even flow that may
parallel the Peninsular Ranges into the eastern San Bernardino
Range. ARW/ARW2/HRRR and therefore HREF solutions (paired back to
account for out of place NAM-NEST), support an additional 2-4"
across south and southwest facing topography east of LA county,
with 1-3" from GFS/ECMWF and CMC (including Gem-Regional). With
potential of .33-.5"/hr rates and these totals over saturated
grounds 0-40cm soil ratios between 70-80% per NASA SPoRT and rain
from the day 1 period, supports an upgrade to Slight Risk where
all these elements overlap within the bulk of the guidance suite.=20
The surrounding Marginal Risk extends to the Mexican border, to
account for the potential of some further slowing down of
solutions, have pulled the Marginal Risk back to the Santa Monica
Range and through much of LA county foothills.

Gallina

Day 3

The Day 3 outlook will be updated by 0830Z.


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!oZ4dMH5FCE4f_m_7ZHvmK0N0Xlsmvm3RmWhhZupPCZLK= iQWf8Yo764hP-al3izSoELOP2bIc$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!oZ4dMH5FCE4f_m_7ZHvmK0N0Xlsmvm3RmWhhZupPCZLK= iQWf8Yo764hP-al3izSoEIIf_brh$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!oZ4dMH5FCE4f_m_7ZHvmK0N0Xlsmvm3RmWhhZupPCZLK= iQWf8Yo764hP-al3izSoEM4ZLEQD$=20


$$




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FOUS30 KWBC 290748
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
247 AM EST Wed Dec 29 2021

Day 1
Valid 12Z Wed Dec 29 2021 - 12Z Thu Dec 30 2021

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE
TENNESSEE VALLEY/SOUTHERN APPALACHIANS AND SOUTHERN CALIFORNIA...

...Tennessee Valley to Central Appalachians...

At the start of the day 1 period, the quasi-stationary front will
continue to sag southward across central and eastern Kentucky and
through the Central Appalachians. Further south, there is a good
possibility there will be ongoing but weakening scattered
convection along the northwest periphery of the synoptic-scale
subtropical ridge in the Bahamas and the impinging aforementioned
northern stream flow across the southern Cumberland Plateau,
southern Appalachians. These cells help to demarcate a ribbon of
enhanced sub-tropical moisture/higher theta-E air originating from
the Western Caribbean, but solidly in place across the Lower
Mississippi River Valley. The next in a series of shortwaves will
be emerging into the south-central Plains and rocketing northeast
through the strong southwest to northeast flow. This wave and
associated buckle in the 3H jet will provide strong synoptic
dynamics within the right entrance region to develop a new surface
wave along the front through the Ozark Plateau into the Tri-Rivers
confluence region and through the Ohio Valley by late day.

Strong moisture flux in the 8-5H layer from the sub-tropic stream
will over-top the return moisture from the Gulf and increase total
PWAT values to 1.5-1.7" across the MS Delta Region into the
Tennessee Valley. Combined with growing unstable environment with
CAPEs of 1500 J/kg into central MS and 750-1000 J/kg into W TN and
the strengthening forcing, strong thunderstorms are expected with
high rainfall rates of 1.5-2"/hr. Strong moisture flux
convergence along/south of the returning front across W TN/N MS
will have increased length to support multiple cells and with deep
layered unidirectional flow, promoting potential for training.=20
Likely due to confluent moisture streams, Hi-Res CAMs are
bifurcating on location of best training/convergence resulting in
lowered HREF Probability values, but guidance does support the
evolution with a slight southward trend, particularly in the
global guidance members. As such, the Slight Risk has been
expanded west and south, centering on area that received 1-2" of
rainfall overnight early Wednesday across N AL. By late evening,
deep layer flow will support multiple rounds across E TN, though
likely to be weaker, in general, due to proximity from the
instability source further upstream. Yet, confidence is higher
across this area for the Slight Risk as HREF probabilities exceed
70% for higher rates/3hr totals.

South across the lower MS River Valley, individual cells may have
a greater potential for cell rotation (see SPC D1 discussion) and
that will support enhanced storm-scale moisture flux convergence
to enhance moisture flux and rainfall efficiency. However, given
orientation to the flow and potential for greater right-hand
turning across the mean deep layer flow should be much less likely
for training across central and southern MS and progressing into
AL through the evening, resulting in a more scattered nature to
flash flooding potential and as such, are encompassed in a broader
Marginal Risk southward.


...Southern California...
An upper-level shortwave will be starting to amplify along the
central California coast throughout the day before swinging more
positive to neutral tilt while starting to pinch off into a closed
low by 30.12z near Point Conception. Models continue show an
increase in spread due to timing and how strong it closes off the
low with the NAM/UKMET a bit slower/deeper and southward relative
the remaining suite and results in a fairly sizable timing
difference with the approach of the cold front/moisture plume.=20=20
Still, all solutions do depict strengthening and backing flow to
support enhanced moisture convergence with 30-40kts of 85H flow
directed toward both the Transverse and Peninsular Ranges with
time. Steepening lapse rates due to the approach of the cold
upper low aloft may further support and areal expansion of weak
instability to 250 J/kg within moderately diffluent flow aloft
supporting increased vertical depth to showers/thunderstorms
resulting in enhanced rain rates of up to .5"/hr even in the lower
elevations. Slow trending upward with moisture to 1" and IVT
values ticking up to 400 to 500 kg/ms further provide confidence
to heavy rainfall signatures even across areas without orographic
enhancement with 1-2" possible.=20

Favorably directed low to mid-level flow will support enhanced
orographic ascent across the Transverse Range while also
supporting WAA to raise snow levels throughout the forecast
period. While the highest peaks of the San Gabriel and San
Bernardino Ranges will continue to have heavy snow, mid-slope
rainfall totals of 2-4+", perhaps over some snow melt and
saturated soils due to 500-600% of normal rainfall over the last
week (per AHPS), mud slide, debris flows and flash flooding are
possible supporting the Slight Risk already in place. Hi-Res
CAM's finer resolution helps to refine the Slight Risk area a bit
more to expand across the Santa Monica Range, Santa Ana, Palomar
mountains as well as mid-slopes of the San Bernadino Range. Slow
NAM/NAM-Nest solutions while of lower probability keep the
westward extent of the Marginal across Santa Barbara county at
this time.=20

Gallina


Day 2
Valid 12Z Thu Dec 30 2021 - 12Z Fri Dec 31 2021

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
SOUTHERN CALIFORNIA...

...Southern California...
By the start of the day 2 period, 30/12z, the shortwave will have
become closed off entering the California Bight. The associated
surface low will move south-southeast through the Channel Islands
and with the 85H low still in proximity, low-level flow and
moisture transport will continue to be directed into southern
California into Day 2. The Hi-Res CAMs along with NAM/NAM-Nest
solutions continue to remain relatively slow mainly due to
stronger that average closed low solutions that delay eastward
progression of the moisture feed/transport. Large scale pattern
suggests next kicker wave upstream is likely to keep the shortwave
progressive and kicking through northern Baja California by early
Friday and the NAM/UKMET are just outlier solutions to this
evolution for overall preference.

With that stated, overall stronger surface wave and therefore
moisture flux transport within the 1" Total PWat narrow plume has
trended slower and allows for longer duration even flow that may
parallel the Peninsular Ranges into the eastern San Bernardino
Range. ARW/ARW2/HRRR and therefore HREF solutions (paired back to
account for out of place NAM-NEST), support an additional 2-4"
across south and southwest facing topography east of LA county,
with 1-3" from GFS/ECMWF and CMC (including Gem-Regional). With
potential of .33-.5"/hr rates and these totals over saturated
grounds 0-40cm soil ratios between 70-80% per NASA SPoRT and rain
from the day 1 period, supports an upgrade to Slight Risk where
all these elements overlap within the bulk of the guidance suite.=20
The surrounding Marginal Risk extends to the Mexican border, to
account for the potential of some further slowing down of
solutions, have pulled the Marginal Risk back to the Santa Monica
Range and through much of LA county foothills.

Gallina

Day 3
Valid 12Z Thu Dec 30 2021 - 12Z Fri Dec 31 2021

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
CENTRAL ARKANSAS THROUGH THE LOWER TENNESSEE VALLEY...

...Lower Mississippi into Lower Ohio/Tennessee River Valleys...
The next in a series of shortwave emerging out of the Southwest
into strong/tightly packed southwest to northeast flow exits into
the Southern Plains very late Friday into early Saturday morning.=20
Unlike the prior waves, it was a bit deeper and closed off
southwest of the southern California coast at the base of the
dominating global scale trof over the Canadian Rockies into the
south. As is typical of this setup, there has been, and continues
to be sizable model variation in resolving critical details, such
as cyclone intensity and depth in latitude. The NAM/UKMET
deepened the wave further west and significantly retarded its
ejection relative to the GFS/ECMWF/CMC and ensemble suite. The
overall pattern and strength of upstream jet axis/kicker shortwave
would suggest the latter is more probable and so has become WPC's preference.=20

Much like prior two systems, the wave will induce another but
slightly stronger surface and low-level response with strong WAA
and moisture flux transport off an open Gulf of Mexico.=20
Internally to this broad Gulf moisture, is a further connection of
higher theta-E air out of the Western Caribbean through the
Yucatan Channel into the Lower Mississippi River Valley. Mid to
upper-level contribution of above normal moisture out continues to
stream out of the sub-tropical Pacific across Texas, resulting in
3 standard deviation of moisture (~1.75" TPW) being advected
through strong WAA response to the approaching by late evening on
Friday into early morning Saturday. The warm front will surge
north across the Mississippi River into the Lower Tennessee Valley
and with strong veered low-level flow and 50-60kts of 85H LLJ,
strong moisture flux convergence along the frontal zone. Deep
layer unidirectional flow will once again support a training
environment at/along the boundary to support a solid potential for
localized heavy rainfall and flash flooding.=20

A Slight Risk of Excessive Rainfall has been placed from Central
Arkansas across W KY/TN. The remaining preferred guidance suggest
a narrower swath of 2"/hr rates and totals 2-4" totals by 01.12z
with isolated 5" values even at this range. While there is pretty
strong agreement in the width of the rainfall footprint, there
remains a 100-150 mile difference northwest to southeast from the
ECMWF to the northwest to a tighter clustering southwest.=20
Preference was given to the tighter clustering/GFS/WPC
Bias-corrected Ensemble but the Slight Risk was broadened at this
time to account for such a spread, as well as trying to account
for swath of worsened ground conditions due to recent rainfall.=20
ECMWF solution would align fairly well to the AHPS 14-day 150-300%
anomaly, while the other solutions would overlap expected forecast
areas from the day 1 period across W TN. So with all this
accounted for, there remains some potential for an upgrade to a
Moderate Risk as the spread reduces and antecedent ground
conditions are accounted for in subsequent issuances. A broad
marginal encompasses the Slight, accounting for downstream
uncertainty into the Ohio Valley or across to the southern
Cumberland Plateau.


...Mid to Lower Slopes of Mogollon Rim of Central Arizona into
Extreme western New Mexico...
Closed low in the base of the larger synoptic trof will already be
progressing along the Arizona/Old Mexico border. Global guidance
denotes plenty of uncertainty in timing due to large differences
in evolution/strength of the closed low through the California
Bight. The NAM/UKMET are notably slower than the GFS/ECMWF/CMC.=20
WPC along with ensemble suite are favoring the more progressive
nature given the upstream evolution across the northern portion of
the trough, so there is some increased confidence. Remaining low
to mid-level moisture transported into the lower Colorado Valley
in the day 2 period will be experiencing veering flow to more
southwest and westerly in the lowest levels, so favorably oriented
to the central Mogollon Rim to eastern extents. Total PWat values
of 1" will be reducing but moisture flux is about 2-2.5 standard
deviations over the mean and IVT values will still be in the
200-400 kg/ms range which is about 1 to 3 standard anomalies over
the 30 year running mean. Up to 1.25" was expected before 31.12z
with an additional 1-2" through the early morning period.

In combination with recent 7-day rainfall anomaly about 300-600%
of normal across central Arizona and north (100-300% south) deep
soil saturation ratios are 70-80%, so 1-3" of additional rain
particularly in complex terrain pose a low-end risk of increased
runoff and flooding. Rain rates are likely to be .25-.33"/hr, so
flash flooding is not particularly probable, but will continue
monitor trend, particularly into Hi-RES window. As such, a
Marginal Risk of Excessive Rainfall was added for areas of the low
to mid-Rim below freezing levels where heavy snow is expected
above and onto the Plateau.=20=20=20=20

Gallina


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!uvqngbBn-taWOz311rLqHZmh2m4phwrqkRQZpAJ52tAw= kbruyUEw8u5xWLGS0Rt1zYO0wpiU$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!uvqngbBn-taWOz311rLqHZmh2m4phwrqkRQZpAJ52tAw= kbruyUEw8u5xWLGS0Rt1zevlee84$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!uvqngbBn-taWOz311rLqHZmh2m4phwrqkRQZpAJ52tAw= kbruyUEw8u5xWLGS0Rt1zWU4QDK-$=20


$$




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