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Mesoscale Discussion 1122
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   Mesoscale Discussion 1122
   NWS Storm Prediction Center Norman OK
   1218 PM CDT Thu Jun 22 2017

   Areas affected...Portions of northeastern OH...western/central
   PA...and western NY

   Concerning...Severe potential...Watch unlikely 

   Valid 221718Z - 221945Z

   Probability of Watch Issuance...20 percent

   SUMMARY...An isolated threat for strong to locally damaging winds
   and marginally severe hail may persist through the afternoon.
   Overall threat should remain too marginal for watch issuance.

   DISCUSSION...17Z objective analysis of surface observations
   indicates a warm front is draped from southeastern lower MI across
   Lake Erie into western NY and northern PA. The airmass along/south
   of the front has become weakly unstable early this afternoon, with
   MLCAPE generally ranging 500-1000 J/kg per 17Z RAP Mesoanalysis.
   Further diurnal heating may allow for MLCAPE values to approach 1500
   J/kg across parts of western/central PA through 20Z. In association
   with a weak mid-level disturbance embedded within strong westerly
   flow at mid/upper levels, isolated thunderstorms have developed
   across eastern Lake Erie into parts of far western NY and
   northwestern PA. One of these cells exhibited brief supercell
   characteristics before weakening across Butler into Armstrong County

   Most of western NY into into western/central PA and northeastern OH
   will remain displaced to the south of stronger mid-level flow across
   the upper Great Lakes into southern Ontario/Quebec and New England.
   Still, around 30-35 kt of westerly flow at 500 mb will support
   similar values of effective bulk shear through the afternoon across
   this region. Additional convective development across northeastern
   OH along the shore of Lake Erie will be possible over the next
   several hours, and any thunderstorms that can remain along/south of
   the front will have the potential to be surface-based. Given the
   marginal shear values, multicells will probably be the dominant
   storm mode, posing a strong to locally damaging wind and perhaps
   marginally severe hail threat. The lack of even stronger instability
   (mainly owing to weak mid-level lapse rates) and shear will likely
   preclude a more robust severe weather threat through the remainder
   of the afternoon. Accordingly, watch issuance is unlikely at this

   ..Gleason/Guyer.. 06/22/2017

   ...Please see for graphic product...


   LAT...LON   40868152 41628174 41858144 42287998 42807896 42467614
               41417621 40487713 40407925 40868152 

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