Storm Prediction Center Mesoscale Discussion 1217

   Mesoscale Discussion 1217
   NWS Storm Prediction Center Norman OK
   0727 PM CDT Sat Jun 20 2026

   Areas affected...eastern Wyoming...western Nebraska
   Panhandle...southwest South Dakota...and far southeast Montana

   Concerning...Severe Thunderstorm Watch 356...

   Valid 210027Z - 210200Z

   The severe weather threat for Severe Thunderstorm Watch 356
   continues.

   SUMMARY...Thunderstorms with a history of measured severe winds will
   weaken as the move northeast this evening. Although a few severe
   wind gusts will be possible in the near term, the overall wind
   threat will weaken with time. A new watch is currently not
   anticipated.

   DISCUSSION...An arc of convection across eastern Wyoming continues
   to fan out as it moves east across the High Plains. These storms
   have had a history of producing significant winds, with multiple
   reports of winds in excess of 80 mph across Converse and Wright
   counties. 

   The non-convectively modified airmass across eastern Wyoming
   features steep low-to-mid-level lapse rates that have supported
   downward momentum transfer and the subsequent strong winds as
   convection moves into them. However, as the storms move farther
   north and east, the airmass becomes increasingly unfavorable for
   severe gusts as instability quickly decreases and low-level lapse
   rates considerably weaken.

   Given the ongoing storms and their recent history, the potential for
   isolated severe wind gusts will continue in the near term. However,
   longer-term, the increasingly unfavorable environment should limit
   downward momentum transfer and the overall severe potential. As
   such, a downstream severe thunderstorm watch is currently not
   anticipated.

   ..Marsh.. 06/21/2026

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

   ATTN...WFO...LBF...UNR...CYS...BYZ...RIW...

   LAT...LON   41600506 43500540 44230602 45110534 45200415 43490242
               41570316 41600506 

   MOST PROBABLE PEAK WIND GUST...55-70 MPH
   MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN