Mesoscale Discussion 1299
   NWS Storm Prediction Center Norman OK
   0316 PM CDT Fri Jul 16 2021

   Areas affected...Southwestern South Dakota and Western Nebraska

   Concerning...Severe potential...Watch possible 

   Valid 162016Z - 162215Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Storms are expected to increase in coverage and intensity
   across southwestern South Dakota and the Nebraska Panhandle over the
   next couple of hours. Uncertainty remains regarding storm coverage
   and evolution, but convective trends will be monitored for the
   possibility of a severe thunderstorm watch.

   DISCUSSION...Despite midlevel heights rising across the region,
   thunderstorms have initiated over the Black Hills in a moist,
   upslope low-level flow regime. With midlevel lapse rates over 8 C/km
   and surface dewpoints in the low 60s F, MLCAPE values are over 1000
   J/kg with continued destabilization expected through the afternoon. 
   While westerly midlevel flow is relatively weak (~25 knots per the
   latest UDX VWP), when coupled with easterly-to-southeasterly
   low-level flow, effective bulk shear is around 30-35 knots, which
   should be sufficient for organized storm modes.  

   Current thinking is that a storm or two may move southeastward off
   of the Black Hills with isolated storm development also possible
   southward along the lee trough/dryline. Storms will initially pose a
   threat for severe hail while remaining discrete, then transition to
   a severe wind threat as outflows merge and grow upscale into
   southeastward-moving clusters.  The increasing south-southeasterly
   low-level jet after ~02Z should further promote storm organization
   and/or new storm development, allowing the severe-weather threat to
   persist after dark.

   ..Jirak/Dial.. 07/16/2021

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

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

   LAT...LON   44060399 44330371 44200248 43630175 42660129 41750111
               41300185 41270295 42090384 42580405 44060399