Mesoscale Discussion 1310

Issued

Jul 17, 2021, 6:54 PM EDT (22:54 UTC)

Expired

Jul 17, 2021, 9:00 PM EDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe thunderstorm watch 382

The Philadelphia radar (KDIX), 122 km from the middle of the area, began a volume at 22:55 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

259 
ACUS11 KWNS 172255
SWOMCD
SPC MCD 172254 
CTZ000-MAZ000-NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-180100-

Mesoscale Discussion 1310
NWS Storm Prediction Center Norman OK
0554 PM CDT Sat Jul 17 2021

Areas affected...portions of central into eastern
Pennsylvania...northern Virginia...Maryland...Delaware...New
Jersey...southeast New York...western Massachusetts...western
Connecticut

Concerning...Severe Thunderstorm Watch 382...

Valid 172254Z - 180100Z

The severe weather threat for Severe Thunderstorm Watch 382
continues.

SUMMARY...The severe threat continues across Severe Thunderstorm
Watch 382. Damaging gusts will remain the primary threat, though an
instance or two of severe hail or a brief tornado cannot be
completely ruled out. The severe threat should diminish with time as
training storms and evening cooling stabilizes the low-level
airmass.

DISCUSSION...MRMS mosaic radar data depicts numerous multicellular
clusters, quasi-organized linear segments, and transient
supercellular storms in progress across much of the northern
Mid-Atlantic into the lower Hudson Valley and southern New England.
Several of these storms have produced damaging gusts, with an
occasional bout of severe hail and brief low-level rotation also
noted. These storms have thrived in a moisture and CAPE-rich
low-level troposphere, with steep low-level lapse rates fostering
damaging gust potential given very warm temperatures. However,
prolonged periods of training storms have resulted in the
overturning of the troposhere, with cool, stable outflow covering
much of the Mid Atlantic. While widespread thunderstorms will likely
continue for at least a few more hours, the severe threat is
expected to gradually wane with time as surface-based buoyant air
becomes scant across the region, and as nocturnal cooling begins in
a couple of hours. 

Still, at least a few more storms supporting damaging gusts are
possible through at least 00Z, particularly in parts of northeast
VA, eastern PA and perhaps southern and eastern NJ, where
cooling/stabilization has been more gradual (surface temperatures
well above 80F), and storm coverage more sparse. In addition, any
storms that interact favorably with convective outflow boundaries
may have a brief, locally higher potential to produce damaging gusts
and perhaps a brief tornado/bout of severe hail. This is especially
the case across southeast NY, where vertical shear is a bit
stronger.

..Squitieri/Guyer.. 07/17/2021

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

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

LAT...LON   38107919 40757704 42537597 42827386 42697331 42177335
            41337380 39877422 39297472 38707581 38227709 38117797
            38107919

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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.