Storm Prediction Center Mesoscale Discussion 1257

   Mesoscale Discussion 1257
   NWS Storm Prediction Center Norman OK
   0310 PM CDT Mon Jun 22 2026

   Areas affected...Eastern Wyoming and adjacent portions of
   Nebraska...South Dakota and far southeast Montana

   Concerning...Severe Thunderstorm Watch 376...

   Valid 222010Z - 222215Z

   The severe weather threat for Severe Thunderstorm Watch 376
   continues.

   SUMMARY...The threat for large hail is slowly increasing across
   eastern Wyoming and far western Nebraska. This threat will gradually
   spread east/southeast over the next few hours.

   DISCUSSION...Latest GOES IR and MRMS data shows steady
   intensification of a trio of supercells near the Sheridan, WY area
   along with more isolated cells near Douglas, WY and near Kimball,
   NE. Across north/northeast WY, low-level moisture is more limited,
   but increasing ascent associated with the left-exit region of the
   300 mb jet aloft continues to overspread the region, aiding in
   mid-level cooling and compensating for the otherwise modest
   moisture. This ascent will continue to promote storm intensification
   through early evening as cells spread east/southeast. Recent
   forecast guidance and SARS estimate hail sizes hint that hail sizes
   will most likely reach into the 1-2 inch range over the next couple
   of hours. 

   Further south, storms in east-central WY to far western NE continue
   to propagate into a plume of richer low-level moisture (dewpoints in
   the low to mid 50s) where a regional SBCAPE maximum is noted (near
   2000 J/kg). Continued low-level moisture advection coupled with
   increasing mid-level flow attendant to the upstream mid-level wave
   should further augment the convective environment over the next few
   hours. By the 22-00 UTC period, the highest SHIP values should
   reside from eastern WY into western NE, suggesting that the greatest
   potential for 2-3 inch hail may manifest across this region.

   ..Moore.. 06/22/2026

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

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

   LAT...LON   41020409 41600441 42690516 43860632 44660688 44990684
               45300658 45400596 45320544 44630469 43310368 42520320
               41580272 41180270 41030280 40820328 40790367 40830389
               41020409 

   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