Mesoscale Discussion 1782

Issued

Sep 23, 2021, 10:30 AM EDT (14:30 UTC)

Expired

Sep 23, 2021, 12:30 PM EDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

20%

Counties Kent County, DE, New Castle County, DE, Sussex County, DE, Caroline County, MD, Cecil County, MD, Wicomico County, MD, Camden County, NJ, Cumberland County, NJ, Gloucester County, NJ, Salem County, NJ, Berks County, PA, Bucks County, PA, Carbon County, PA, Chester County, PA, Delaware County, PA, Lehigh County, PA, Montgomery County, PA, Northampton County, PA, Philadelphia County, PA

The Dover AFB radar (KDOX), 73 km from the middle of the area, began a volume at 14:32 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.

717 
ACUS11 KWNS 231431
SWOMCD
SPC MCD 231430 
NJZ000-PAZ000-MDZ000-DEZ000-231630-

Mesoscale Discussion 1782
NWS Storm Prediction Center Norman OK
0930 AM CDT Thu Sep 23 2021

Areas affected...Portions of the Delmarva Peninsula into
southeastern PA and NJ

Concerning...Severe potential...Watch unlikely 

Valid 231430Z - 231630Z

Probability of Watch Issuance...20 percent

SUMMARY...Sporadic strong to damaging wind gusts may continue
through the early afternoon. Watch issuance remains unlikely.

DISCUSSION...A north-south oriented band of storms should continue
to make slow eastward progress across the Delmarva Peninsula over
the next couple of hours. This activity is occurring along a surface
cold front, with a moist low-level airmass present to its east. As
filtered diurnal heating occurs through the remainder of the
morning, the boundary layer should gradually destabilize, with
around 500-1000 J/kg of MLCAPE eventually developing. Even so,
multiple limiting factors remain apparent, including poor mid-level
lapse rates tempering updraft strength, stronger deep-layer shear
likely remaining confined to the cool side of the surface front, and
nearly meridional flow above 1 km AGL limiting opportunity for the
band of storms to develop eastward more quickly.

Recent inland observations across eastern MD show that gusty outflow
winds within the band have remained generally below 40 mph. While
sporadic strong to damaging wind gusts may still occur as the line
continues to advance slowly eastward, this threat should remain
quite isolated/marginal. Finally, there is some low-level shear
present ahead of the line from far eastern MD into DE and
southeastern PA/western NJ. Recent VWPs from KDOX and KDIX show
around 25-30 kt of 0-1 km shear, with about 150-200 m2/s2 of 0-1 km
SRH also present. Even with the less than favorable orientation of
the line, an embedded low-level circulation capable of producing a
brief tornado appears possible. Regardless, the overall severe
threat is expected to remain rather marginal owing the previously
mentioned limiting factors, and watch issuance is unlikely at this
time.

..Gleason/Hart.. 09/23/2021

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

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

LAT...LON   38387589 38737592 39577616 40177615 40697590 40967569
            40907512 40167470 39537477 38937497 38557521 38307546
            38387589

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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.