Mesoscale Discussion 0644
   NWS Storm Prediction Center Norman OK
   0243 PM CDT Wed May 20 2020

   Areas affected...eastern MT

   Concerning...Severe potential...Watch likely 

   Valid 201943Z - 202115Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Thunderstorms are expected to increase across eastern MT
   over the next couple of hours. Large hail and locally damaging wind
   gusts will be possible with these storms, and a watch will likely be
   needed by 21z.

   DISCUSSION...Early-day showers and cloudiness has lifted northward
   toward the MT/SK border, allowing temperatures to quickly warm into
   the mid 70s to low 80s across much of eastern MT. Strong
   southeasterly low level winds ahead of a surface low just east of
   the Big Horn mountains have allowed surface dewpoints to increase
   into the mid 50s to near 60 F beneath steep midlevel lapse rates
   (7.5-8.5 C/km). Thunderstorms have already developed over the higher
   terrain of the Beartooth/Absaroka mountains, and an increase in CU
   has been noted in visible satellite imagery beneath scattered
   mid-upper level clouds. Increasing ascent is currently spreading
   into southern MT as a lead shortwave impulse ejects
   north/northeastward from the upper low centered over the northern
   Great Basin. This should result in additional storms developing over
   the higher terrain of southeast MT in the next couple of hours, as
   well as additional development further east across the High Plains
   of eastern MT as weak capping erodes.

   Strong effective shear will support organized cells/clusters with
   long, straight forecast hodographs indicating large hail potential
   when combined with thermodynamic characteristics across the region.
   Inverted-v sub-cloud thermodynamic profiles suggest strong downburst
   winds also will be possible. Clusters of storms will track generally
   northward during the evening and should mainly stay confined to
   eastern MT and far northwest SD.

   ..Leitman/Guyer.. 05/20/2020

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...BIS...UNR...BYZ...GGW...TFX...

   LAT...LON   44930532 45040735 45150822 45440890 45850916 46630950
               48980943 49090417 46800398 45230386 44990407 44930532