Mesoscale Discussion 1597
   NWS Storm Prediction Center Norman OK
   0227 PM CDT Thu Aug 27 2020

   Areas affected...Portions of southern and eastern Montana into
   northern and eastern Wyoming

   Concerning...Severe potential...Watch possible 

   Valid 271927Z - 272200Z

   Probability of Watch Issuance...60 percent

   SUMMARY...Severe threat is gradually increasing across portions of
   the northern High Plains. Large hail and damaging winds are expected
   to be the primary threats, with a tornado or two possible with any
   storm that can be become more long-lived and supercellular in
   nature. Trends are being monitored for the issuance of a WW over
   parts of the region.

   DISCUSSION...Agitated CU are rapidly developing across western WY in
   response to adequate diurnal heating and deep-layer ascent
   associated with an approaching mid-level shortwave that is beginning
   to overspread the northern High Plains. Modest flow aloft with the
   associated mid-level shortwave is expected to contribute to 50+
   knots of effective bulk shear, more than adequate for supporting
   updraft organization and sustaining mid-level rotation. Forecast
   1000-1500 J/kg MLCAPE downstream of the CU field (driven by 60+F
   dewpoints per latest METARs and 8+ C/km low and mid-level lapse
   rates per 17Z RAP) should support robust convective development
   across the northern High Plains over the next few hours. 

   RAP forecast soundings depict relatively straight to slightly
   cyclonically curved hodographs, suggesting that multicellular
   clusters and splitting supercells will be the dominant mode of
   convection, as also supported by HREF and the last few runs of the
   HRRR. Large hail and damaging winds are expected to be the primary
   threats. Given the magnitude of deep-layer shear expected, one or
   two sustained right-moving supercells, capable of producing a couple
   significant (around 2 inch diameter) hailstones and perhaps a
   tornado cannot be completely ruled out.

   ..Squitieri/Grams.. 08/27/2020

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

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

   LAT...LON   42871044 44230968 45760762 46460641 46460507 46330448
               45730419 44930413 44290421 43360457 42800527 42600629
               42430794 42871044