SPC AC 271721

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1221 PM CDT Mon Jul 27 2020

   Valid 281200Z - 291200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   NEW ENGLAND AND THE NORTHERN MID ATLANTIC COAST REGION...

   ...SUMMARY...
   Strong thunderstorms may impact a corridor from New England into the
   northern Mid Atlantic Coast region Tuesday, accompanied by at least
   some risk for potentially damaging wind gusts.

   ...Synopsis...
   A mature cyclone will be centered over Ontario early Tuesday
   morning. Modest eastward progress of this cyclone is anticipated
   throughout the day as several compact, low-amplitude shortwave
   troughs move through the stronger mid-level flow at its base.
   Occluded surface low associated with this system will be centered
   over far northwest Quebec but the cold front attendant to this low
   is expected to extend through western New York southwestward all the
   way into northern OK. Anticipated progression of the parent cyclone
   will help push the northern/eastern portions of the front through
   much of New England while it remains predominantly stalled
   elsewhere. 

   Farther west, a shortwave trough is forecast to move through the
   central/northern Rockies into the northern/central High Plains.
   Progression of this system will result in a dampening of the upper
   ridging previously in place across the northern and central High
   Plains. 

   Generally weak flow aloft will persist throughout the southern tier
   of the CONUS. Within this weak flow, a convectively augmented
   vorticity maximum will drift eastward/southeastward across northern
   portions of the southern Plains. 

   ...New England into Mid Atlantic region...
   Temperatures ahead of the front are forecast to range from the 80s
   across ME to the 90s across the Mid-Atlantic states. Dewpoints are
   expected to be in the low 70s areawide. These warm and moist
   conditions will support moderate buoyancy, despite the lack of steep
   mid-level lapse rates/cooling aloft. Stronger mid-level flow will
   lag behind the front, minimizing the overlap between the stronger
   vertical shear and better buoyancy. Even so, some overlap does
   appear probable, particularly across eastern portions of New
   England. In these areas, storm coverage is expected to be lower than
   those farther south but the overall environment suggests these
   storms could become strong/organized enough to produce damaging wind
   gusts. 

   Buoyancy and storm coverage is expected to increase southward into
   the Mid-Atlantic. Weak vertical shear will likely preclude storm
   organization, but isolated damaging wind gusts are still possible as
   a result of heavy precipitation loading and modest storm motions.

   ...Upper MS Valley...
   Modest moisture advection is anticipated ahead of a subtle shortwave
   trough and attendant cold front. This increased low-level moisture
   coupled with steep low-level lapse rates will result in modest
   instability, despite generally poor mid-level lapse rates. Deep
   northwesterly flow aloft over the region is forecast to strengthen
   with height, result in moderate vertical shear. Storm initiation
   remains in question, precluding any probabilities with this outlook,
   but a conditional severe risk exists. Probabilities may be needed in
   future outlooks if confidence in storm initiation increases.

   ..Mosier.. 07/27/2020

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