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Mesoscale Discussion 1319
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MD 1319 graphic

   Mesoscale Discussion 1319
   NWS Storm Prediction Center Norman OK
   1203 PM CDT Tue Jul 20 2021

   Areas affected...Parts of Upstate New York and adjacent portions of

   Concerning...Severe potential...Watch possible 

   Valid 201703Z - 201930Z

   Probability of Watch Issuance...60 percent

   SUMMARY...An organizing cluster of thunderstorms over parts of
   southern Ontario likely will begin impacting the upper St. Lawrence
   Valley and Lake Ontario vicinity by 3-5 PM EDT, accompanied by
   increasing potential for damaging wind gusts.

   DISCUSSION...Associated with larger-scale mid/upper troughing
   digging in the St. Lawrence Valley/lower Great Lakes region, forcing
   for ascent with a lead speed maximum (30-50 kts in the 500-300 mb
   layer) appears to be providing support for an ongoing, well
   organized cluster of thunderstorms across southeastern Ontario. 
   Perhaps aided by an associated strengthening surface cold pool, this
   activity has accelerated some (up to 40 kt) over the past couple of
   hours, and may reach the Ottawa vicinity by around 19Z.

   Along trailing outflow into the vicinity of its intersection with a
   southward advancing cold front, additional thunderstorm development
   and intensification is now also well underway.  Supported by
   moderate southeasterly low-level inflow of moist air characterized
   by CAPE of 1000-2000 J/kg, this seems likely to continue with the
   evolution of another upscale growing and organizing cluster/segment
   possible.  This may begin impacting the Ontario shores of Lake
   Ontario into the Watertown vicinity as early as 20-21Z, perhaps a
   bit earlier and more substantively than suggested by the latest
   Rapid Refresh.

   Although low-level wind fields are generally weak, the effective
   downward mixing of higher momentum air aloft, associated with the
   well developed/maturing organized convective system and associated
   surface cold pools, probably will be accompanied by increasing
   potential for strong gusts at least approaching severe limits.

   ..Kerr/Hart.. 07/20/2021

   ...Please see for graphic product...


   LAT...LON   44618000 44557856 44917736 45307677 45407578 44937319
               44477329 44107422 43797486 43407580 43167760 43377902
               44238068 44618000 

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