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Mesoscale Discussion 1650
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   Mesoscale Discussion 1650
   NWS Storm Prediction Center Norman OK
   0250 PM CDT Mon Aug 30 2021

   Areas affected...Southwestern South Dakota and portions of far
   northern Nebraska and eastern Wyoming

   Concerning...Severe potential...Watch possible 

   Valid 301950Z - 302145Z

   Probability of Watch Issuance...40 percent

   SUMMARY...A few severe thunderstorms, including supercells, with the
   potential for damaging winds and hail are possible this
   afternoon/evening. A weather watch is being considered.

   DISCUSSION...As of 1930 UTC, visible imagery showed deepening
   updrafts across the Black Hills of far western South Dakota and
   eastern Wyoming. Developing within a weakly forced upper air regime,
   additional surface heating and weak upslope flow are expected to
   support continued destabilization and subsequent thunderstorm
   development this afternoon. 

   The modified 18z UNR sounding shows an environment potentially
   conducive to organized multicells and supercells, with 1700 J/kg of
   MLCAPE and 31 kt effective shear. Although weak, inhibition of -40
   to -50 J/kg remains across the region, with low-level cumulus still
   absent across far southwestern South Dakota. However, this will
   likely be overcome in the next couple of hours as convective
   temperatures in the mid to upper 80s F are breached by strong
   surface heating. Isolated thunderstorm development is possible by
   late afternoon as the incipient updrafts move out of the Black Hills
   and onto the surrounding High Plains. Favorable CAPE/shear profiles
   and mid-level lapse rates in excess of 8 C/km will support the
   potential for large hail and damaging wind gusts, especially with
   any supercells. 

   While the environment will remain potentially favorable for severe
   weather, uncertainty remains on the exact spatial coverage of storms
   within the weak forcing regime. Hi-res guidance suggests that at
   least isolated storms will develop and track southeastward into
   northwestern Nebraska this evening. Given the favorable CAPE/shear
   overlap an isolated severe risk for wind and hail would be possible.
   Convective trends are being monitored for a possible weather watch
   despite the uncertainty on storm coverage.

   ..Lyons/Grams.. 08/30/2021

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

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

   LAT...LON   44790333 44600236 44130157 43750127 43380097 43020090
               42770100 42420145 42280212 42270267 42590352 42980384
               43420411 44030425 44440421 44670399 44790333 

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Page last modified: August 30, 2021
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