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Mesoscale Discussion 1819
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   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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