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Mesoscale Discussion 1353
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   Mesoscale Discussion 1353
   NWS Storm Prediction Center Norman OK
   0252 PM CDT Wed Jul 19 2017

   Areas affected...extreme south central South Dakota into into
   extreme north central Nebraska

   Concerning...Severe potential...Watch unlikely 

   Valid 191952Z - 192115Z

   Probability of Watch Issuance...20 percent

   SUMMARY...At least isolated thunderstorm development may occur over
   SD near the SD-NE border. Should storms develop, a few instances of
   large hail and downburst winds will be possible. Given expected
   limited storm coverage, a WW issuance will probably not be needed
   unless convective trends dictate otherwise.

   DISCUSSION...As of mid afternoon a cluster of cumulus was observed
   increasing in vertical depth along a stalling convectively enhanced
   front across south central SD. This convection appears to be
   increasing where plume of deeply mixed hot air intersects the front
   and western fringe of deeper moisture. Forcing on the mesoscale is
   weakening with time as the progressive shortwave trough and its
   attendant low-level jet shifts east of this region. However, the
   deep mixing promoted by strong diabatic warming and frontal
   convergence might be sufficient to initiate isolated storms this
   evening. Steep lapse rates, moderate instability and 30-40 kt 0-6 km
   shear will support potential for updraft rotation and a threat for a
   few instances of large hail and downburst winds. Limiting factor for
   a WW issuance is expected isolated nature of the convection due to
   the presence of a warm elevated mixed layer and relatively weak
   forcing.

   ..Dial/Hart.. 07/19/2017

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

   ATTN...WFO...FSD...OAX...ABR...LBF...UNR...

   LAT...LON   43700085 43599848 43019786 42769828 43260093 43700085 

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Page last modified: July 19, 2017
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