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Mesoscale Discussion 1394
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   Mesoscale Discussion 1394
   NWS Storm Prediction Center Norman OK
   1212 PM CDT Sat Jul 22 2017

   Areas affected...Portions of MD...DE...northern VA...southern
   PA...Washington DC

   Concerning...Severe potential...Watch unlikely 

   Valid 221712Z - 221945Z

   Probability of Watch Issuance...20 percent

   SUMMARY...A small, remnant convective system will spread across
   parts of the Mid-Atlantic through the afternoon, posing a risk for
   at least isolated wind damage. While present indications are that
   Watch issuance is unlikely, convective and environmental trends will
   continue to be monitored across the area.

   DISCUSSION...The leading convective line of a persistent MCS is
   crossing the Appalachians, and should continue along its eastward
   track across portions of the Mid-Atlantic region through the
   afternoon hours. This activity lies well in advance of a mid-level
   speed maximum crossing the lower Great Lakes region, and principally
   south of a broader belt of enhanced westerly flow aloft.

   The LWX VAD wind profile is indicating only around 10-20 kt of flow
   in the 1-2-km layer, suggesting that convective momentum transport
   will be quite limited, as the remnant system maintains some
   semblance of pseudo-organization amid modest 25-30 kt of effective
   shear. Regardless, diurnally strengthening baroclinicity along the
   gust front owing to surface heating ahead of the convective line has
   resulted in a slight uptick of convective cores, as convective
   inflow destabilizes. With surface temperatures breaching 90F amid
   dewpoints in the lower 70s, adequate buoyancy may exist for
   sufficiently robust convective cores to produce sporadic wind damage
   eastward toward the Atlantic Coast. 

   Modest deep shear, the lack of a more substantial convectively
   driven cold pool, weak low-level flow, and weak mid-level lapse
   rates should all limit the severe risk. Regardless, if a stronger,
   convectively-driven cold pool were to eventually evolve from
   convection as it spreads east of the Appalachians and encounters
   steeper low-level lapse rates, prospects for Watch issuance could
   increase.

   ..Cohen/Grams.. 07/22/2017

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

   ATTN...WFO...PHI...AKQ...CTP...LWX...

   LAT...LON   38957835 39497757 39887670 39637552 38917519 38457539
               38247582 38457743 38697827 38957835 

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