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Mesoscale Discussion 1287
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   Mesoscale Discussion 1287
   NWS Storm Prediction Center Norman OK
   0348 PM CDT Tue Jul 11 2017

   Areas affected...the eastern Dakotas and western portions of MN

   Concerning...Severe potential...Watch likely 

   Valid 112048Z - 112215Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Convective initiation is forecast over the next 1-2 hours.
   Severe thunderstorms capable of large to very large hail, severe
   gusts, and possibly a tornado are forecast this evening.  A
   convective watch is likely in the next 1-2 hours.

   DISCUSSION...Visible satellite imagery shows several areas of
   clumping/agitated cumulus.  Weak low level confluence is implied by
   streamline analysis across east-central SD near Huron where a
   cumulus field is present as of 2040Z.  Other areas where storm
   initiation may occur may evolve from where the boundary layer is
   probably more deeply mixed near the MO River near the SD/ND border
   and farther north to the north of Jamestown, ND.  

   RAP forecast soundings show a very unstable airmass (3000-4000 J/kg
   MLCAPE) from east-central SD into east-central ND within a moist
   axis with upper 60s-lower 70s degrees F dewpoints.  Southerly
   low-level winds veering and increasing with height to 35-kt in the
   mid levels is resulting in around 40-45 kt effective shear.  Once
   updrafts break the cap, rapid severe storm development is forecast. 
   Large hail will be the initial risk.  Hail diameters in excess of 2
   inches in diameter are possible with the most intense supercells.  A
   risk for a tornado may develop towards evening dependent on both
   convective mode and storms moving into an environment near the ND/MN
   border and over west-central MN where hodographs are slightly
   larger.  Severe gust potential will likely increase as storms
   congeal this evening.

   ..Smith/Thompson.. 07/11/2017

   ...Please see for graphic product...


   LAT...LON   44049864 45929831 48029932 48719886 48809744 48159598
               47209526 46029511 44599530 43729609 43719781 44049864 

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