Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
SPC AC 241643
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1143 AM CDT Mon Aug 24 2020
Valid 241630Z - 251200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER
MIDWEST AND FLORIDA PANHANDLE/FAR SOUTHERN ALABAMA...
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.
...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
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
...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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