Mesoscale Discussion 1308

Issued

Jul 17, 2021, 4:38 PM EDT (20:38 UTC)

Expired

Jul 17, 2021, 6:15 PM EDT

In force

97 min

Issued by

the Storm Prediction Center

Concerning

Severe thunderstorm watch 382

The Philadelphia radar (KDIX), 130 km from the middle of the area, began a volume at 20:37 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

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995 
ACUS11 KWNS 172039
SWOMCD
SPC MCD 172038 
MAZ000-RIZ000-CTZ000-NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-DCZ000-VAZ000-WVZ000-172215-

Mesoscale Discussion 1308
NWS Storm Prediction Center Norman OK
0338 PM CDT Sat Jul 17 2021

Areas affected...Portions of the Mid-Atlantic into southern New
England

Concerning...Severe Thunderstorm Watch 382...

Valid 172038Z - 172215Z

The severe weather threat for Severe Thunderstorm Watch 382
continues.

SUMMARY...A threat for mainly damaging wind gusts will continue
through the remainder of the afternoon.

DISCUSSION...Multiple clusters of loosely organized storms have
developed this afternoon across parts of the Mid-Atlantic into
southern New England. One area of perhaps the best damaging wind
potential should exist across parts of western MD and central PA in
the short term. Here a broken line of storms will likely continue to
move eastward over the next couple of hours. The airmass downstream
of this activity should remain favorable for strong/gusty convective
downdrafts to reach the surface and cause mainly tree damage.
Farther south into northern VA and vicinity, the low/mid-level flow
quickly weakens per recent VWPs from KLWX. Accordingly, storms have
struggled to maintain intensity with southward extent across the
Mid-Atlantic. Still, an isolated damaging wind threat should
continue across this region in the short term with any storms that
can persist given the steep low-level lapse rates and moderate
boundary-layer instability present.

Slightly stronger deep-layer shear is present along/near a warm
front located across southern NY and into southern New England.
Occasional supercells may occur in this regime, with around 30-35 kt
of effective bulk shear per latest mesoanalysis estimates. Some
marginal hail and perhaps a brief tornado will remain possible near
the warm front in the short term, but damaging wind gusts should
continue to be the main threat through the remainder of the
afternoon across a majority of Severe Thunderstorm Watch 382.

..Gleason.. 07/17/2021

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

ATTN...WFO...BOX...OKX...ALY...PHI...BGM...CTP...LWX...

LAT...LON   38217899 39497871 40087836 40767773 41127743 41867713
            42507635 42717485 42697333 42697224 42587166 42057144
            41357179 41287236 40507379 39357566 38447651 38177805
            38217899

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The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.