Mesoscale Discussion 1668

Issued

Sep 1, 2021, 11:03 AM EDT (15:03 UTC)

Expired

Sep 1, 2021, 1:30 PM EDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...tornado watch likely

Chance of a watch

95%

The Dover AFB radar (KDOX), 64 km from the middle of the area, began a volume at 15:06 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.

• Tornado Watch 482Sep 1, 11:40 AM EDT
• Tornado Watch 483Sep 1, 12:40 PM EDT

101 
ACUS11 KWNS 011503
SWOMCD
SPC MCD 011503 
NJZ000-MDZ000-DEZ000-PAZ000-VAZ000-DCZ000-WVZ000-011730-

Mesoscale Discussion 1668
NWS Storm Prediction Center Norman OK
1003 AM CDT Wed Sep 01 2021

Areas affected...northern Virginia into southeast Pennsylvania and
New Jersey

Concerning...Severe potential...Tornado Watch likely 

Valid 011503Z - 011730Z

Probability of Watch Issuance...95 percent

SUMMARY...Storms are likely to increase in coverage and intensity
near a front from northern Virginia into New Jersey. Damaging winds
and a few tornadoes appear likely.

DISCUSSION...Surface analysis shows a low over eastern WV with a
front extending east/northeastward into southern NJ. Extensive
clouds exist over much of the region, but relative clearing exists
across eastern NC and VA toward the Delmarva. The strongest
instability is coincident with the mid 70s F dewpoints near the zone
of clearing. While temperatures aloft are warm, this is still
resulting in substantial instability.

Low-level shear is currently maximized along and just north of the
stationary front from southern PA into NJ, as well as along an axis
from the WV Panhandle southward across west-central VA. 0-1 SRH
values up to 100 m2/s2 exist in the higher theta-e air mass, which
is sufficient for a tornado risk.

As the low continues slowly northeastward, and warm advection
persists near the rain-reinforced stationary front, effective SRH is
expected to concentrate from northern VA across MD, southeast PA and
NJ. Showers now forming along a line from central VA into northeast
NC near the instability gradient are expected to gradually deepen,
and a couple supercells may evolve out of this line of convection.
Otherwise, storms are likely to gradually increase in coverage and
intensity east of the low as it shifts into southeast PA and NJ be
evening. Both damaging winds and few tornadoes will be possible. In
addition, the PA/NJ portion of the front is expected to shift north,
and this may bring the severe risk toward Long Island this evening.

..Jewell/Grams.. 09/01/2021

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

ATTN...WFO...PHI...AKQ...CTP...LWX...

LAT...LON   38497497 37957521 37547557 37227697 37237744 37497769
            38197791 38667826 39047818 39857665 39987619 39987589
            39927549 39687513 39357477 39027478 38847497 38497497

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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.