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ACUS11 KWNS 191723
SWOMCD
SPC MCD 191722=20
WYZ000-192115-

Mesoscale Discussion 1876
NWS Storm Prediction Center Norman OK
1222 PM CDT Tue Oct 19 2021

Areas affected...portions of eastern/central Wyoming

Concerning...Heavy snow=20

Valid 191722Z - 192115Z

SUMMARY...Ongoing moderate to heavy precipitation will gradually
transition to snow this afternoon across central and eastern WY
impacting travel conditions. Snow rates above 1 inch per hour with
occasional reductions in visibility due to heavy and blowing snow
are possible.

DISCUSSION...As of 1700 UTC, WV imagery showed the core of a
well-defined upper low was located near the western CO, UT and WY
borders. To the north and east of the upper low, large-scale forced
ascent was supporting the development of widespread stratiform
precipitation across much of western and central Wyoming.=20

Over the last hour, regional radar imagery showed additional banded precipitation developing ahead of the low from the vicinity of KRIW
to KLAR. Likely in response to increasing lift near a region of
strong 700 mb frontogenesis, as well as orographic ascent,
additional precipitation development/intensification within this
band appears likely over the next several hours. Surface
temperatures across much of Wyoming remain just above freezing
suggesting initial precip type will be rain below 7k feet. However,
as column saturation takes place, dynamic cooling and increasing
low-level cold advection from surface pressure falls ahead of the
upper low should result in a transition to snow by early afternoon.=20

As the upper low continues eastward along the CO/WY border, strong
height falls (60-90 DM/12 hr) should support moderate to heavy snow
within the developing frontogenetic band as it wraps
north/northwestward around the low. Hi-res guidance and regional
model soundings show support for snow rates near or exceeding 1 inch
per hour through the afternoon driven in part by steep mid-level
lapse rates near the cold core of the upper low. Additionally, weak
convective buoyancy as well as negative EPV (indicative of
slant-wise instability) suggest some potential for convective
elements/banding favorable for locally higher snow rates through the
afternoon. While the transition from rain to snow is likely to be
gradual, moderate to heavy snow appears likely across much of
central and eastern Wyoming through the afternoon. The potential for
heavy snow and gusty north winds may result in occasional blowing
snow/low visibility disruptive to travel. Weakening ascent and
increasingly dry mid-level air should end the heavy snow threat as
the upper low shifts to the northeast this evening.

..Lyons/Bunting.. 10/19/2021

...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!sJ7uJWczCX5UYne0G8ApJWmMXJTvPMgsLn5cSFqWEKo6cbaA-s514T1icxQXztOGkD4aDBlg$=
for graphic product...

ATTN...WFO...UNR...CYS...RIW...

LAT...LON 43590504 43330483 42870478 42530471 42240473 41850484
41670516 41580560 41700621 42100671 42460760 42580804
42860833 43260838 43730775 43820720 43810640 43790598
43590504=20



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