Mesoscale Discussion 468

Issued

Apr 29, 2021, 4:52 PM EDT (20:52 UTC)

Expired

Apr 29, 2021, 7:15 PM EDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

5%

Counties Kent County, DE, New Castle County, DE, Caroline County, MD, Cecil County, MD, Kent County, MD, Queen Anne's County, MD, Talbot County, MD, Atlantic County, NJ, Cape May County, NJ, Cumberland County, NJ, Gloucester County, NJ, Salem County, NJ

The Dover AFB radar (KDOX), 44 km from the middle of the area, began a volume at 20:56 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.

256 
ACUS11 KWNS 292052
SWOMCD
SPC MCD 292052 
NJZ000-DEZ000-PAZ000-MDZ000-292315-

Mesoscale Discussion 0468
NWS Storm Prediction Center Norman OK
0352 PM CDT Thu Apr 29 2021

Areas affected...portions of eastern Maryland...Delaware...and
southern New Jersey

Concerning...Severe potential...Watch unlikely 

Valid 292052Z - 292315Z

Probability of Watch Issuance...5 percent

SUMMARY...Some severe threat may accompany any storm that manages to
develop over the next few hours, though storm initiation remains
highly uncertain at this time. Any severe threat that develops is
expected to be sparse and a WW issuance is not anticipated.

DISCUSSION...A surface low continues to gradually intensify while
moving east-northeast along the PA/NY border. Aloft, a mid-level
trough impinges on the Atlantic Seaboard. Latest Mesoanalysis
depicts a weak impulse embedded in the 500 mb flow over the WV/VA
border, which is associated with a 60+ kt mid-level jet streak and
is overspreading a surface lee-trough axis. Though weak, enough
deep-layer ascent across portions of the Mid Atlantic may suffice to
support the development and sustenance of a couple thunderstorms
through the late afternoon and early evening hours.

Ahead of the surface lee-trough, 40-50 kts of southwesterly 925-850
mb flow is overspreading the upper Mid Atlantic/lower Hudson Valley.
Though veering with height is not particularly pronounced, the
stronger low-level flow overspread by the aforementioned mid-level
jet streak is supporting 50-70 kts of effective bulk shear. LWX,
DOX, and DIX VWPs over the past couple of hours have also shown
modestly curved hodographs with 200-300 m2/s2 0-3km SRH. Enough
diurnal heating has supported surface temperatures reaching near 80
F, that combined with low to mid 60sF dewpoints has contributed to
500 J/kg MUCAPE (much which is surface-based) despite mediocre
mid-level lapse rates. Given the mixed boundary layer, latest
Mesoanalysis has depicted much of the 0-3km SRH to be the effective
inflow layer. As such, any storms that can develop and sustain
themselves will have the potential to become organized and
potentially rotate. Damaging gusts and large hail would be the main
threats. Nonetheless, the severe threat is highly conditional given
low confidence in storms initiating. If initiation does occur,
storms are expected to remain very isolated, with a WW issuance
being unlikely.

..Squitieri/Hart.. 04/29/2021

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

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

LAT...LON   38687568 38687607 38797626 39117645 39417647 39757596
            39827544 39767503 39687469 39477436 39147463 38897474
            38687568

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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.