SPC MD 1362


MD 1362 Image

Mesoscale Discussion 1362
NWS Storm Prediction Center Norman OK
1204 PM CDT Fri Jul 31 2020

Areas affected...Mid-Atlantic Region

Concerning...Severe potential...Watch unlikely 

Valid 311704Z - 311900Z

Probability of Watch Issuance...20 percent

SUMMARY...Isolated strong-to-severe wind gusts will be possible this
afternoon with the strongest thunderstorms. Coverage of the
thunderstorm threat should limit the need for a severe thunderstorm

DISCUSSION...A belt of modest mid-level flow exists atop a frontal
boundary draped across portions of central Virginia. To the north of
this boundary, a combination of northerly low-level flow, widespread
cloud cover, and ongoing showers have kept surface temperatures in
the 60s and 70sF. Along and south of the aforementioned boundary,
surface southerly low-level flow and pockets of clearing skies o
allowed surface temperatures to warm into the 80s to low 90sF. Given
surface dewpoints across the region in the low-to-mid 70sF, a strong
north-to-south gradient in CAPE exists, ranging from around 250 J/kg
of most-unstable CAPE in the vicinity of Washington D.C. to around
3000 J/kg of most-unstable CAPE across southern Virginia.

Although forcing mechanisms for sustained, robust deep convection
are nebulous, the combination of sufficient convergence along the
aforementioned surface-boundary and weak large-scale ascent
associated with small-scale perturbations within the modest
mid-level flow will lend itself for isolated to scattered
thunderstorm development this afternoon. The degree of instability
and deep-layer shear on the order of 30 knots will be sufficient for
clusters of multi-cell thunderstorms capable of producing isolated
strong-to-severe wind gusts. Modest mid-level lapse rates (on the
order of 6 C/km) should limit the overall hail potential.

Given the expected isolated coverage of the convection, a severe
thunderstorm watch is not currently anticipated this afternoon, but
conditions will continue to be monitored.

..Marsh/Bunting.. 07/31/2020

...Please see www.spc.noaa.gov for graphic product...


LAT...LON   38147998 38687802 38547559 37637516 36627633 35827987

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