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Mesoscale Discussion 1108
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   Mesoscale Discussion 1108
   NWS Storm Prediction Center Norman OK
   0138 PM CDT Wed Jun 21 2017

   Areas affected...Portions of central/southern PA...MD...far eastern
   WV...DC...far northern VA...DE...NJ...southern NY...and CT

   Concerning...Severe potential...Watch unlikely 

   Valid 211838Z - 212115Z

   Probability of Watch Issuance...5 percent

   SUMMARY...Strong/gusty winds associated with isolated thunderstorms
   this afternoon may produce sporadic tree damage. A watch is not
   anticipated for this marginal severe threat.

   DISCUSSION...Isolated thunderstorms have developed over the past
   hour or so along a remnant front across central PA. Visible
   satellite imagery shows partly to mostly sunny conditions to the
   east of this isolated convection (across eastern PA/northern NJ into
   southern NY/CT), and surface temperatures have generally warmed into
   the 80s away from the coast. Although the low-level airmass is not
   overly moist along/south of the remnant front per area 18Z surface
   observations and 12Z soundings, it is sufficient to support weak
   instability of generally 250-750 J/kg (MLCAPE). Some additional
   diurnal heating through late afternoon may locally boost MLCAPE to
   around 1000 J/kg.

   Recent VWPs from KCCX depict nearly unidirectional westerly flow
   strengthening quickly to around 45-50 kt at 5 km, and the
   mid/upper-level flow likely increases further through the remainder
   of the troposphere given the presence of a belt of enhanced flow
   over this region per latest short-term guidance and water vapor
   satellite imagery. Related effective bulk shear of 40-50 kt should
   support some convective organization even with instability expected
   to remain modest owing mainly to poor mid-level lapse rates.
   Steepening low-level lapse rates owing to continued diurnal heating
   combined with the strong shear may result in an isolated
   strong/gusty convective downdraft wind risk. However, nebulous
   large-scale forcing for ascent, weak instability, and generally
   isolated thunderstorm coverage will likely keep the overall severe
   threat marginal. Therefore, watch issuance is not expected at this

   ..Gleason/Weiss.. 06/21/2017

   ...Please see for graphic product...


   LAT...LON   40657944 40847805 40997660 41117494 41957371 41977287
               41817218 41477196 40897223 40627291 40437381 39867399
               39637409 38927477 38787498 38677632 39077820 39417951
               40367985 40657944 

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