Mesoscale Discussion 1215

Issued

Jul 9, 2021, 4:35 PM EDT (20:35 UTC)

Expired

Jul 9, 2021, 6:30 PM EDT

In force

115 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

The Philadelphia radar (KDIX), 129 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

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

677 
ACUS11 KWNS 092036
SWOMCD
SPC MCD 092035 
NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-092230-

Mesoscale Discussion 1215
NWS Storm Prediction Center Norman OK
0335 PM CDT Fri Jul 09 2021

Areas affected...portions of southeast New York into eastern
Pennsylvania...far northeast Maryland...western New Jersey

Concerning...Severe potential...Watch possible 

Valid 092035Z - 092230Z

Probability of Watch Issuance...40 percent

SUMMARY...The severe threat continues to increase across portions of
the Mid Atlantic this afternoon. Damaging gusts remain the primary
threat with the stronger, longer-lived storms. Conditions will
continue to be monitored for the need of a Severe Thunderstorm Watch
issuance.

DISCUSSION...Multicellular clusters, evident via MRMS mosaic radar
imagery, have demonstrated small, bow-type structures over the past
hour or so, with some damaging gusts reported. These storms are
progressing in an environment characterized by widespread, poor
mid-level lapse rates, but with 7+ C/km 0-3km lapse rates (evident
via 20Z mesoanalysis and 19Z RAP forecast soundings). The
aforementioned low-level lapse rates atop upper 60s to 70 F surface
dewpoints are contributing to 1000-1500 J/kg MLCAPE amid 40+ kt
effective bulk shear. These bulk shear vectors are oriented roughly
perpendicular to the smaller linear segments. As such, storms are
expected to continue supporting damaging gust potential through the
remainder of the diurnal heating cycle. It is unclear how widespread
the damaging gust threat will be through the remainder of the
afternoon. Conditions will continue to be monitored for the need of
a Severe Thunderstorm Watch issuance should it become evident that
more widespread damaging gusts will become likely.

..Squitieri/Bunting.. 07/09/2021

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

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

LAT...LON   39667526 39547579 39607655 40087747 40257770 41647647
            42497520 42377471 41867430 41277423 40427469 39737526
            39667526

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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.