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Mesoscale Discussion 1238
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   Mesoscale Discussion 1238
   NWS Storm Prediction Center Norman OK
   0552 PM CDT Wed Jul 05 2017

   Areas affected...The Dakotas and adjacent portions of Minnesota

   Concerning...Severe potential...Watch possible 

   Valid 052252Z - 060115Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Through 7-9 PM CDT, severe weather potential may remain
   largely confined to isolated/widely scattered storm development
   across parts of western North Dakota into western and central South
   Dakota.  The initiation of storms across north central/eastern North
   Dakota into central Minnesota remains uncertain, but more probable
   after dark than before.

   DISCUSSION...Moderate to strong potential instability appears to
   have developed across portions of the region, mainly where boundary
   layer moisture is seasonably high, generally on the leading edge of
   a plume of warm elevated mixed layer air advecting eastward across
   the northern Plains, ahead of a weakening cold front just south of
   the international border area.  Largest CAPE (in excess of 3000
   J/kg) appears focused within a narrow corridor east of Minot ND,
   through areas near/northeast of Fargo ND, Alexandria and St. Cloud
   MN.  This is generally within the overlap of the stronger boundary
   layer heating, and the higher boundary layer moisture content, where
   mid-level warming probably is maintaining capping.

   Well to the south of a vigorous short wave impulse digging across
   northern Manitoba into northwestern Ontario, large-scale forcing for
   ascent appears generally weak.  And ongoing thunderstorm development
   across parts of western North Dakota into north central South Dakota
   appears largely where convective temperatures  have been reached
   within the drier, hotter and more deeply mixed boundary layer
   environment.  Even though CAPE supporting this activity is
   considerably more modest than in the more moist boundary layer air,
   veering wind profiles with height beneath 30-40 kt northwesterly 500
   mb flow is contributing to strong shear.  This could continue to
   enhance activity as it propagates southeastward, with a risk for
   locally strong surface gusts and some hail into the 00-02Z time,
   before the boundary layer begins to decouple.

   Otherwise, the possible initiation of thunderstorms within the more
   moist and potentially unstable environment remains more unclear.  It
   is possible that any such development may await nocturnal southerly
   low-level jet strengthening associated with boundary layer
   decoupling, generally during the 02-05Z time frame.

   ..Kerr/Thompson.. 07/05/2017

   ...Please see for graphic product...


   LAT...LON   48519681 47009436 45309421 44979608 44479765 43279954
               44130187 45130269 46190217 47550292 48500326 49750173

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