Storm Prediction Center Mesoscale Discussion 2149

   Mesoscale Discussion 2149
   NWS Storm Prediction Center Norman OK
   0143 PM CDT Thu Aug 27 2026

   Areas affected...portions of the Black Hills into northwestern and
   west-central Nebraska

   Concerning...Severe potential...Watch likely 

   Valid 271843Z - 272045Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Thunderstorms forming on the Black Hills will evolve
   southeastward through the evening, bringing a risk for large to very
   large hail and severe wind gusts.

   DISCUSSION...Latest surface analysis depicts a corridor of low-60s F
   dewpoints across northwestern Nebraska and southwestern South Dakota
   that have been maintained by moist southerly/southeasterly low-level
   flow. Combined with strong diurnal heating and weak ascent
   associated with a subtle mid-level wave progressing southeastward
   out of eastern Montana, convective initiation is likely across the
   Black Hills within the next 1-2 hours. Supercells will be the
   initial storm mode owing to strong northwesterly flow aloft and
   40-45 kts of effective shear. While some uncertainty remains
   regarding convective evolution (particularly supercell longevity and
   the potential for eventual upscale growth), very steep mid-level
   lapse rates and elongated hodographs sampled by the 18z UNR observed
   sounding will support a risk for large to very large hail (up to
   2-3+ inches in diameter) with any sustained supercells. Severe to
   perhaps significant severe wind gusts of 65-75 mph may also occur
   with these supercells, with a greater threat for severe gusts likely
   to accompany any convective cluster that eventually evolves as this
   activity progresses southeastward. Regardless of the exact storm
   mode evolution, a Severe Thunderstorm Watch will likely be needed
   once convective development currently noted over the Black Hills
   matures.

   ..Chalmers/Mosier.. 08/27/2026

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

   ATTN...WFO...LBF...UNR...CYS...

   LAT...LON   44280348 43540157 43030059 42710030 42330028 41850058
               41500113 41320192 41520251 42000294 43020345 44050394
               44310382 44280348 

   MOST PROBABLE PEAK WIND GUST...65-80 MPH
   MOST PROBABLE PEAK HAIL SIZE...2.00-3.50 IN