SPC AC 291729

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1229 PM CDT Tue Jun 29 2021

   Valid 301200Z - 011200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR MUCH OF
   MASSACHUSETTS AND PARTS OF EAST-CENTRAL NEW YORK...

   ...SUMMARY...
   Strong to severe thunderstorms capable of scattered damaging gusts
   are probable Wednesday afternoon and evening over parts of the
   Northeast.

   ...Northeast...
   A large-scale mid-level trough over southeast Canada into the Great
   Lakes/Northeast will move little, while a belt of strong
   southwesterly flow will extend from the lower Great Lakes across the
   Northeast.  In the low levels, a weak surface low over the lower St.
   Lawrence Valley will migrate slowly eastward.  Ahead of the surface
   low and an attendant eastward-moving frontal zone, a moisture-rich
   boundary layer will feature surface dewpoints in the upper 60s to
   lower 70s.  A weak cap atop a swelling cumulus field during the late
   morning will lead to scattered thunderstorms developing by 12-2pm
   EDT over western NY with other activity developing over northern New
   England and into the upper OH Valley.  Strong heating is forecast to
   lead to a moderate to very unstable airmass (MLCAPE ranging from
   1500-3000 J/kg) with effective shear (30-45 kt) supporting organized
   storms.  A mix of embedded cells and linear convection will likely
   evolve as storms grow upscale into one or more main convective
   clusters/lines during the afternoon into the early evening.  The
   greatest combination of shear/buoyancy is forecast from parts of NY
   eastward into southern New England within a corridor of steep 0-2 km
   lapse rates.  It is within this focused area where the potential for
   strong to severe gusts (50-70 mph) is highest and the threat for
   damaging gusts is greatest.  The activity will likely wane/diminish
   by the mid evening hours as the loss of heating leads to storm
   weakening.

   ...OH Valley...
   Weaker flow fields compared to farther northeast will likely limit
   the amount of storm organization with scattered thunderstorms that
   develop during the day.  Nonetheless, strong heating within a
   moist/destabilizing airmass will lead to locally strong/severe
   thunderstorms developing by the early/mid afternoon.  Several of the
   stronger cores/bowing segments will be capable of damaging gusts.

   ..Smith.. 06/29/2021

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