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ACUS11 KWNS 101922
SWOMCD
SPC MCD 101922=20
ILZ000-TNZ000-KYZ000-MOZ000-ARZ000-102145-
Mesoscale Discussion 1978
NWS Storm Prediction Center Norman OK
0122 PM CST Fri Dec 10 2021
Areas affected...Much of central and northeastern Arkansas through
southeastern Missouri and adjacent portions of southern
Illinois...western Kentucky and Tennessee
Concerning...Severe potential...Watch likely=20
Valid 101922Z - 102145Z
Probability of Watch Issuance...95 percent
SUMMARY...Discrete supercell supercell development appears
increasingly probable by 4-6 PM CST, accompanied by the risk for
severe hail and tornadoes, including increasing potential for a
couple of strong tornadoes by early evening.
DISCUSSION...A short wave impulse of subtropical eastern Pacific
origin continues to accelerate northeastward across Kansas and
Oklahoma, and is forecast to reach the mid/lower Missouri Valley
vicinity by early evening. Mid/upper forcing for ascent and
elevated moisture return preceding this feature have contribute to
weak high-based convection and light rain in a corridor across
eastern Oklahoma into the lower Missouri Valley, while low-level
moisture from the Gulf of Mexico gradually deepens across the lower
Mississippi Valley into parts of the southeastern Great Plains. The
deeper low-level moisture return is being aided by a branch of
stronger southerly flow across the northwestern Gulf coast vicinity
into the Ozark Plateau. This appears to include a 40-45 kt speed
maximum around 850 mb, across the upper Texas coastal plain into the
Ark-La-Tex vicinity.
Through 21-00Z, model output continues to generally indicate that
this speed maximum will rapidly propagate northeastward into the
Ozark Plateau through middle Mississippi/lower Ohio Valley vicinity,
while strengthening to 50+ kt in a corridor from near Little Rock AR
into the Missouri Bootheel vicinity. It appears that deepening
boundary-layer moisture and increasing mixed-layer CAPE along this
corridor will coincide with weakening inhibition associated with a
transition from broadly anticyclonic to cyclonic mid-level flow.=20
This is expected to allow for the initiation of at least scattered
discrete storm development, as southwesterly flow in the 700-500 mb
layer also strengthens to 60-80+ kt.
This regime likely will become increasingly conducive to the
development of supercells, with the potential to produce severe hail
initially, along with at least some risk for tornadoes. Backing of
surface winds toward a south to south-southeasterly component by 00Z
may gradually contribute to enlarging, clockwise-curved low-level
hodographs increasingly conducive to tornadoes, a couple of which
may become strong.
..Kerr/Thompson.. 12/10/2021
...Please see
https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!uTEZmw0fBTIk5yQGa9WzGpEHlTgsEMPfM_-Bt0-qNfmQglukW0hpuDMZm4tjPWDQrUVKfrrr$=
for graphic product...
ATTN...WFO...PAH...MEG...LSX...LZK...SGF...
LAT...LON 36769201 38068994 37408898 36288919 34749081 34519233
35259322 36769201=20
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