Storm Prediction Center Mesoscale Discussion 1254

   Mesoscale Discussion 1254
   NWS Storm Prediction Center Norman OK
   1229 PM CDT Mon Jun 22 2026

   Areas affected...Southeast Wyoming into adjacent portions of
   Nebraska...Colorado...South Dakota...and Montana

   Concerning...Severe potential...Watch likely 

   Valid 221729Z - 221930Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Thunderstorm development appears likely in the next couple
   of hours across southeast Wyoming. Storms that develop will likely
   mature into supercells posing a threat for very large hail; watch
   issuance will likely be needed as convection begins to develop.

   DISCUSSION...Latest GOES imagery shows a small zone of deepening
   cumulus within a weak upslope flow regime along the eastern slopes
   of the Laramie and Big Horn Mountains in Wyoming. Latest forecast
   guidance suggests that lingering mixed-layer inhibition will be
   largely eroded as temperatures warm into the mid to upper 70s. With
   observed temperatures in the vicinity of the deepening cumulus
   currently in the upper 60s and low 70s, it appears likely that
   further growth will occur with increasing probability for convective
   initiation over the next couple of hours - especially as broad-scale
   ascent ahead of an upstream wave continues to overspread the region.


   Regional VWPs are sampling 35-45 knot mid-level flow, which should
   increase through late afternoon as the mid-level disturbance
   continues to the southeast. This will yield elongated hodographs
   with effective shear values on the order of 40-50 knots by late
   afternoon, which will promote splitting supercells capable of
   producing very large hail (possibly as high as 2.5 to 3 inches based
   on sounding analogs). Large hail, as well as brief tornado,
   potential appears highest across southeast WY into northeast
   CO/western NE where richer low-level moisture will support higher
   buoyancy and more intense updrafts and some effective SRH is noted
   in latest RAP mesoanalyses. Trends are being monitored for the onset
   of more substantial/widespread initiation, and watch issuance will
   likely be needed once this becomes apparent.

   ..Moore/Hart.. 06/22/2026

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

   ATTN...WFO...UNR...BOU...CYS...BYZ...RIW...

   LAT...LON   41040280 40490278 39840289 39590311 39480349 39450403
               39500439 39730463 40170468 40510465 41030475 41240477
               41800491 42580541 42900570 43580623 44400676 44930699
               45230685 45270612 45120552 44710501 44140455 43370401
               42610357 41460294 41040280 

   MOST PROBABLE PEAK TORNADO INTENSITY...85-110 MPH
   MOST PROBABLE PEAK WIND GUST...55-70 MPH
   MOST PROBABLE PEAK HAIL SIZE...2.00-3.50 IN