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 041624
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1124 AM CDT Fri Aug 04 2017
Valid 041630Z - 051200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE LOWER
GREAT LAKES/UPPER OHIO VALLEY AND INTO THE ADJACENT MOUNTAINS...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK...AND EXTENDING SOUTHWESTWARD INTO PORTIONS OF THE
CENTRAL GULF COAST STATES/SOUTHERN APPALACHIANS...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
CENTRAL HIGH PLAINS VICINITY...
Scattered severe storms are expected this afternoon and evening from
Ohio and West Virginia across Pennsylvania and New York and
vicinity. Isolated severe storms may also evolve this afternoon and
evening across portions of the central High Plains and vicinity.
Cyclonic flow aloft is forecast to expand across the U.S. today, to
encompass nearly the entire country by the end of the period.
Within the broader cyclonic flow field, a pronounced short-wave
trough will move east across the Great Lakes/Ohio Valley region
through the day, and gradually impinge on the Northeast through the
second half of the period.
At the surface, a low is currently analyzed over the eastern upper
Michigan vicinity, with a cold front trailing south across eastern
lower Michigan and western Ohio, and then southwest across western
Kentucky/western Tennessee/southern Arkansas into northern Texas.
As the front advances steadily eastward/southeastward, a zone of
increasing thunderstorm activity focused along/ahead of the front is
forecast to evolve through this afternoon and evening.
A gradual increase in convective coverage/intensity is ongoing at
this time from the Lake Erie vicinity south-southwest into eastern
parts of Kentucky and Tennessee, near and ahead of the advancing
surface cold front. Additional afternoon heating -- particularly
into New York/Pennsylvania/West Virginia just ahead of band of mid
and high clouds preceding the surface front -- will support
additional/gradual destabilization, and thus continued support for
further convective increases. Aiding the anticipated increase in
convective intensity/organization will be a gradual strengthening of
the flow field aloft across the warm sector, as the upper trough
crossing the Great Lakes pivots east and acquires slight negative
tilt. The overall result will be a gradual increase in severe risk
through the afternoon, with potential for hail and locally damaging
winds. Wind risk may continue into the evening -- particularly if
storms can grow upscale into a few organized bands, but eventual
diurnal stabilization of the boundary layer into the evening
suggests the risk will gradually diminish after dark.
...The central High Plains area...
Weak post-frontal southeasterly flow is indicated at this time
across the High Plains area, on western fringes of a 1023 mb surface
high currently centered over southeast Nebraska. The southeast flow
will maintain a ribbon of mid to upper 50s dewpoints across the
central High Plains area, which combined with daytime heating will
support development of 1000 to 1500 J/kg mixed-layer CAPE this
afternoon. Expect development of isolated storms over higher
terrain to commence by mid afternoon, with a few storms intensifying
locally -- aided by amply strong shear as a result of moderate
mid-level northwest flow atop the low-level southeasterlies. Along
with local risk for hail, gusty/potentially damaging winds may occur
locally as well, particularly if storms can grow upscale into a
small cluster or two that shift southeast into/across
lower-elevation areas of eastern Colorado and the Nebraska Panhandle
into the evening hours.
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