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SPC MD 1819


MD 1819 Image

Mesoscale Discussion 1819
NWS Storm Prediction Center Norman OK
0237 PM CDT Thu Sep 22 2022

Areas affected...northeastern Wyoming and southeastern Montana

Concerning...Severe potential...Watch unlikely 

Valid 221937Z - 222130Z

Probability of Watch Issuance...5 percent

SUMMARY...Scattered thunderstorms developing in the Powder River
Basin and the higher terrain of WY/MT are forecast to move eastward
with a risk for marginally severe hail and isolated strong to severe
wind gusts this afternoon. A weather watch is not expected.

DISCUSSION...As of 1930 UTC, afternoon visible imagery and lightning
data showed increasing convective development ongoing along the
higher terrain of northern WY and southeastern MT. Ahead of a deep
upper low, broad diffluent mid-level flow and cool temperatures
aloft are helping to destabilize a cool but relatively moist airmass
across the northern Rockies. With moderate upslope flow and surface
dewpoints in the 40s and low 50s F, SPC mesoanalysis shows
sufficient buoyancy for strong updrafts has developed (500-1000 J/kg
MLCAPE). As storms continue to mature through the afternoon, 40 kt
of effective shear should support some organization into clusters
and perhaps a few weak supercells as they detach from the higher
terrain. Moderate to strong upper level flow and fast storm motions
may support a risk for a isolated strong to localized severe wind
gusts. Cool mid-level temperatures and steepening lapse rates may
also support a risk for marginally severe hail, and or large amounts
of small hail, especially with any sustained supercells.

The primary limiting factor for additional storm organization is the
weaker buoyancy. As storms mature and detach from the terrain of the
Big Horns, orographic lift will weaken and inhibition should
increase with eastern extent. While isolated hail/wind will be
possible with the strongest storms this afternoon, the localized
threat should remain limited enough that a weather watch is not

..Lyons/Grams.. 09/22/2022

...Please see for graphic product...


LAT...LON   43430823 45340902 46080891 46680728 46750553 46430464
            45970425 45230408 44800418 44290490 44070528 43660623

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