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Mesoscale Discussion 1360
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MD 1360 graphic

   Mesoscale Discussion 1360
   NWS Storm Prediction Center Norman OK
   1036 AM CDT Thu Jul 20 2017

   Areas affected...Portions of western NY...northwestern PA...far
   northeastern OH

   Concerning...Severe potential...Watch possible 

   Valid 201536Z - 201730Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Convection approaching the area ahead of a cold front and
   destabilization are expected to support a threat for severe wind
   gusts and marginally severe hail developing in the next few hours. A
   Severe Thunderstorm Watch may be needed in the next few hours.

   DISCUSSION...Ongoing convection, currently sub-severe, over the
   Niagara Peninsula will continue to spread east over the Niagara
   Frontier region. An eastward-moving cold front now stretching from
   southern Ontario across western Lake Erie should support new
   thunderstorm development in the next few hours.  Although the 12Z
   BUF sounding shows very little instability and numerous dry layers
   with a history of subsidence, the 12Z DTX sounding sampled a region
   of air with high PW and somewhat steep 800-600 mb lapse rates that
   appear to have not been overturned from the widespread convective
   activity farther west yesterday and this morning.  This air mass is
   expected to be drawn east and northeast ahead of the front during
   the day.  The ongoing convection is expected to mostly remain north
   of this region of instability in the next hour or two, but the
   southern edge of the convection now approaching the Buffalo area
   could regenerate toward the end of this period as it emerges into
   Erie, Genesee, and Wyoming Counties.

   Furthermore, substantial heating now underway over the western NY
   Southern Tier region into northwest PA and northeast OH, in the
   midst of 68-73F surface dewpoints, should add to the instability in
   the next few hours and eventually contribute to MUCAPE values of
   1500-2500 J/kg.  Deep, bulk vertical wind shear of 40 kt over
   northeast OH to around 60 kt, as seen in KBUF 88D VAD wind profiles,
   and likely enhanced by convective outflow from the remnant
   convective system over the Ohio Valley, is more than sufficient for
   convective organization, including line segments and supercell
   structures.  Given the enhancement in low-level lapse rates expected
   as the atmosphere destabilizes, severe wind gusts will be the
   primary threat, with marginally severe hail possible in the more
   organized storms.  The need for a Watch remains uncertain owing to
   uncertainties in coverage, but signs of convective organization
   could increase the likelihood that a Watch would be needed.

   ..Coniglio/Cohen/Hart.. 07/20/2017

   ...Please see for graphic product...


   LAT...LON   43357861 43357802 43267756 42977664 42347634 41857676
               41557781 41327859 41107937 41118041 41348106 41748127
               42368033 42867958 43357861 

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