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Mesoscale Discussion 1395
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   Mesoscale Discussion 1395
   NWS Storm Prediction Center Norman OK
   0218 PM CDT Sat Jul 22 2017

   Areas affected...Portions of central and southern Ohio...and West
   Virginia

   Concerning...Severe potential...Watch possible 

   Valid 221918Z - 222145Z

   Probability of Watch Issuance...60 percent

   SUMMARY...Portions of the middle and upper Ohio Valley region to the
   central Appalachians are being monitored for some increase in the
   severe risk and possible Watch issuance.

   DISCUSSION...Visible imagery indicates a gradual deepening of
   convective plumes along a band of isentropic ascent from the Miami
   Valley of Ohio to central Ohio, atop modifying outflow air deposited
   by earlier rounds of convection. The northeastward transport of hot
   and moist boundary-layer conditions continues into this corridor,
   with temperatures rising through the 80s to locally lower 90s amidst
   dewpoints in the middle 70s along its southern periphery. Despite
   modest mid-level lapse rates -- tempering the acceleration of
   updrafts -- substantial buoyancy (MLCAPE around 2000-3500 J/kg) is
   developing northeastward into the Dayton-Columbus-Lancaster
   corridor. This should be a general zone of additional convective
   deepening in the short-term -- along the southern periphery of an
   MCV crossing northern Ohio and an MCV crossing the Whitewater Valley
   of east-central Indiana. Convective development may further be aided
   by ascent preceding a mid-level speed maximum approaching from the
   west-northwest.

   Sufficient mid-level flow accompanying the speed maximum --
   augmented by tightened height gradients around the MCVs -- is
   yielding 30-40 kt of effective shear in support of potentially
   organized convective structures. Convection could grow into one or
   two forward-propagating clusters/MCSs as it moves toward/across the
   Ohio River and eventually central Appalachians into the evening. The
   Wilmington Ohio VAD wind profile indicates 30-40 kt of flow in the
   1-3-km layer, with modest veering of winds with height, suggesting
   that sufficient low-level flow and vertical shear will support
   convective momentum transport and storm-scale circulations capable
   of enhancing surface wind gusts. Scattered damaging wind gusts may
   eventually occur, if more organized cold pools were to congeal.

   There is still considerable uncertainty regarding the details of
   convective evolution, owing to numerous diffuse, antecedent outflow
   boundaries governing/complicating convective evolution. The timing
   and track of greater damaging-wind risk are still uncertain, though
   the area will continue to be monitored for a gradually increasing
   severe risk.

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

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

   ATTN...WFO...LWX...PBZ...RLX...ILN...

   LAT...LON   38568297 39248428 39628454 39918363 39938204 39558038
               38997921 38347977 38298135 38568297 

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Page last modified: July 22, 2017
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