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Mesoscale Discussion 1386
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   Mesoscale Discussion 1386
   NWS Storm Prediction Center Norman OK
   0746 PM CDT Fri Jul 21 2017

   Areas affected...Western into southeast ND...North-central SD

   Concerning...Severe Thunderstorm Watch 428...

   Valid 220046Z - 220215Z

   The severe weather threat for Severe Thunderstorm Watch 428
   continues.

   SUMMARY...The severe threat continues in and near WW 428. A
   conditional threat also exists further north near the international
   border.

   DISCUSSION...Convection across the western portion of WW 428 has
   thus far been more isolated compared to areas further east, but a
   few stronger cells have recently evolved across far south-central ND
   into north-central SD. Buoyancy and shear across the region are
   sufficient for supercell development, and a threat of large hail and
   locally damaging winds will persist for the next 1-2 hours with the
   strongest discrete cells. Later this evening, increasing SBCINH will
   result in a weakening trend for any remaining discrete cells, though
   any clusters that grow somewhat upscale may persist a little longer
   with an attendant threat for locally damaging wind. 

   Additional convection just outside of WW 428 across McLean and
   Mercer counties has thus far failed to intensify, but a conditional
   wind/hail risk will exist if any supercell can evolve from that
   activity. 

   Meanwhile, further north toward the international border, the
   airmass north of a surface boundary has largely been unaffected by
   convection further to the south, and moderate buoyancy has
   developed, with MLCAPE in the 1500-2500 J/kg range per recent
   mesoanalyses. Easterly flow at the surface veering to westerly aloft
   is resulting in effective shear of 45-55 kt, more than sufficient
   for supercells. A cluster of strong storms is ongoing near the
   international border now and may persist for awhile this evening,
   with a corresponding threat of severe hail/wind and perhaps a
   tornado.

   ..Dean.. 07/22/2017

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

   ATTN...WFO...FGF...FSD...ABR...BIS...UNR...

   LAT...LON   44219983 45530198 47620245 48510267 49040253 48989847
               48389842 48039993 47139987 47169857 47209730 46079758
               44919872 44189866 44219983 

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