SPC AC 271544

   Day 3 Convective Outlook CORR 1
   NWS Storm Prediction Center Norman OK
   1044 AM CDT Sun Sep 27 2020

   Valid 291200Z - 301200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF THE MID-ATLANTIC STATES...

   CORRECTED FOR  VALID DAY OF FORECAST IN SUMMARY.

   ...SUMMARY...
   Isolated severe thunderstorms are possible across portions of the
   Mid-Atlantic States on Tuesday.

   ...Synopsis...
   A deep upper trough is forecast to extend from Quebec into the Lower
   MS Valley early Tuesday morning. An upper low embedded within this
   larger trough is expected to gradually move from the middle MS
   Valley southeastward through the Southeast. Southerly mid-level flow
   will increase ahead of this low from GA through the Mid-Atlantic.
   Progression of this upper low will aid in the development of a
   modest surface low along a front initially extending from the
   Mid-Atlantic southwestward through the central FL Panhandle. This
   surface low will likely track northeastward along the front while
   the front gradually moves eastward. Some deepening of this surface
   low is possible, resulting in modest moisture advection amid
   southerly/southeasterly surface wind.

   This overall pattern evolution will place a modestly moist and
   unstable air mass across the Mid-Atlantic states ahead of the
   approaching cold front (and parent upper trough). Previously
   mentioned strengthening low to mid-level winds ahead of the
   approaching upper low atop modest southerly/southeasterly surface
   winds will contribute to at least moderate vertical shear. While
   some uncertainties remain, including the amount of destabilization
   as well as the strength of the surface low and frontal position, the
   environment appears likely to support at least low severe potential.
   Refinements to this outlook area are likely in subsequent forecasts.

   ..Mosier.. 09/27/2020

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