SPC AC 241944

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0244 PM CDT Mon Aug 24 2020

   Valid 242000Z - 251200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
   THE UPPER MIDWEST AND NORTHEAST GULF COAST...

   ...SUMMARY...
   One or more clusters of storms capable of producing large hail,
   damaging winds, and an isolated tornado are expected across parts of
   the Upper Midwest late this afternoon into tonight.  Other more
   isolated severe storms may occur this afternoon from the
   Mid-Atlantic into New England, and along the Gulf Coast with
   Tropical Storm Marco.

   ...Discussion...
   Only one minor change was made to the previous convective outlook. 
   This outlook update included parts of southwest GA in 5-percent
   tornado probabilities near a southwest-northeast oriented surface
   wind shift.  The 18z Tallahassee observed sounding showed a modest
   hodograph with southeast flow at the surface.  Near and north of the
   wind shift shows surface winds backed to the east and
   east-northeast, thereby resulting in a larger hodograph and a narrow
   corridor where the potential for low-level storm rotation may
   maximize.  Elsewhere, the forecast appears on track.

   ..Smith.. 08/24/2020

   .PREV DISCUSSION... /ISSUED 1143 AM CDT Mon Aug 24 2020/

   ...Upper Midwest today into tonight...
   Few changes warranted to the Slight Risk across the region as some
   uncertainty still remains in this forecast regarding thunderstorm
   timing through tonight. There is potential for surface-based
   thunderstorm development later this afternoon as surface
   temperatures warm into the 90s along and south of the
   outflow-reinforced front. If storms do form on this boundary this
   afternoon, the environment will conditionally favor supercells
   capable of producing large hail/damaging winds, and perhaps a
   tornado. A more certain/higher probability scenario is for storms to
   form along/just north of the boundary across Minnesota/western
   Wisconsin this evening as warm/moist advection increases. Large hail
   along with some damaging wind potential can be expected as storms
   increase in coverage and develop east-southeastward into Wisconsin
   tonight.

   ...Gulf Coast/Georgia...
   While Tropical Storm Marco will tend to weaken (reference NHC for
   latest details), a zone of sufficiently strong low-level shear will
   persist along the Gulf coast to support a low-end supercell/tornado
   threat today primarily in coastal areas from the Florida/far
   southern Alabama into southern Georgia. Farther east, residual 30-40
   kt low/mid-level flow and daytime heating/destabilization on the
   east edge of the thicker cloud shield could support isolated strong
   outflow gusts today across other parts of Georgia.

   ...South Florida today into tonight...
   Tropical Storm Laura will skirt the south coast of Cuba and emerge
   over the southeast Gulf of Mexico early Tuesday -- please see latest
   NHC advisories for further details. Strengthening of the gradient
   flow on the north side of the tropical cyclone will result in
   sufficient vertical shear for isolated rotating storms within the
   outer northern convective bands later today into tonight across the
   Keys, where an isolated tornado will be possible. Other
   thunderstorms with more a gusty wind threat may occur across the
   Florida Peninsula primarily through the afternoon.

   ...New England into parts of the Mid-Atlantic this afternoon...
   In advance of a deepening midlevel trough over Ontario, a series of
   subtle perturbations will move eastward from the OH Valley/lower
   Great Lakes toward New England and the Mid-Atlantic through tonight.
   Low/mid-level flow/vertical shear will remain rather modest across
   much of this area (effective bulk shear of 20-30 kt), but daytime
   heating and terrain circulations will again initiate at least widely
   scattered thunderstorms this afternoon from Virginia northward into
   New England. MLCAPE ranging from 1000 J/kg north to 2000 J/kg south,
   as well as DCAPE in the 750-1000 J/kg range, will support multicell
   clusters capable of producing isolated damaging gusts this
   afternoon.

   ...Western/northern Nevada into southeast Oregon...
   Enhanced mid-level flow/ascent will exist across the region in
   association with a shortwave trough. While a combination of
   clouds/smoke may also slow surface heating somewhat, modest CAPE and
   well-mixed boundary layer profiles will support the possibility of
   strong/gusty outflow winds with thunderstorms.

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