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Mesoscale Discussion 1336
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MD 1336 graphic

   Mesoscale Discussion 1336
   NWS Storm Prediction Center Norman OK
   0401 AM CDT Tue Jul 18 2017

   Areas affected...Southern North Dakota and northern South Dakota

   Concerning...Severe potential...Watch unlikely 

   Valid 180901Z - 181030Z

   Probability of Watch Issuance...5 percent

   SUMMARY...Potential for marginal severe hail/surface gusts is
   expected to diminish through the 5-6 AM time frame.

   DISCUSSION...The ongoing organized mesoscale convective system
   appears to have been supported by an area of enhanced low-level warm
   advection to the immediate cool side of a stalled surface frontal
   zone near the North/South Dakota border area.  The Rapid Refresh has
   been consistent suggesting that this forcing will weaken during the
   next couple of hours, which seems likely to lead to diminishing
   convective trends, despite the current strength and organization of
   the convective system.  As 20-30 kt westerly deep layer mean flow
   contributes to a continuing eastward progression of the convective
   system, the latest objective instability analysis suggests that
   system-relative inflow should become increasingly stable as activity
   advances toward areas near/north of Aberdeen.

   Warm advection above the outflow/outflow reinforced front in the
   wake of the convective system may support continuing or renewed
   convective development near the state border area through daybreak. 
   However, any appreciable risk for marginally severe hail and surface
   gusts seems limited to the lead cluster.

   ..Kerr/Thompson.. 07/18/2017

   ...Please see for graphic product...


   LAT...LON   46499906 46579764 46589724 45919644 45099809 45239957
               45829958 46499906 

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