Mesoscale Discussion 1313

Issued

Jul 22, 2020, 1:45 PM EDT (17:45 UTC)

Expired

Jul 22, 2020, 3:45 PM EDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

60%

The Brookhaven radar (KOKX), 113 km from the middle of the area, began a volume at 17:45 UTC, the scan nearest the moment this went out.

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• Severe Thunderstorm Watch 394Jul 22, 2:55 PM EDT

310 
ACUS11 KWNS 221746
SWOMCD
SPC MCD 221745 
MAZ000-CTZ000-NYZ000-NHZ000-VTZ000-NJZ000-PAZ000-221945-

Mesoscale Discussion 1313
NWS Storm Prediction Center Norman OK
1245 PM CDT Wed Jul 22 2020

Areas affected...portions of eastern PA...NJ...southern NY and
southern New England

Concerning...Severe potential...Watch possible 

Valid 221745Z - 221945Z

Probability of Watch Issuance...60 percent

SUMMARY...Scattered thunderstorms will increase in coverage and
intensity through the afternoon. Strong, locally damaging gusts will
be possible with these storms into this evening.

DISCUSSION...A broad area of deepening cumulus continues to develop
across portions of eastern PA/NJ northeastward into southern New
England ahead of a shortwave vorticity max. At the surface, a warm
front extends from central NY east/southeast into CT/RI. South of
the front, surface dewpoints are mainly in the 70s F and strong
heating has allowed temperatures to warm into the mid to upper 80s
F. As a result, a tongue of MLCAPE from 500-1500 J/kg resides from
eastern PA and NJ northward into southern NY and western CT. The
warm front should progress northward a bit more through the
afternoon and at least weak destabilization is expected as far north
as southern VT/NH into western/central MA. 

In addition to weak to moderate instability, moderate deep shear
resides over the region, and effective bulk shear around 35-45 kt
should overspread the entire MCD area by late afternoon. Some
uncertainty with regards to convection initiation remains, largely
due to weak forcing across the area. A vorticity max further east
near Lakes Erie/Ontario should spread eastward with time, but
initial convective development may be largely driven by diurnal
processes, especially over southern portions of the MCD area from
far southern NY/Long Island southward into NJ. Nevertheless, the
overall environment should support organized cells and clusters,
once they develop. Midlevel lapse rates will remain modest, but
strong heating has resulted in steep low level lapse rates south of
the warm front, and PW values greater than 1.75 inches will further
aid in strong downburst potential. 

While timing of convection remains a bit uncertainty, at least
sporadic instances of severe gusts and locally damaging winds are
expected into the evening hours, and a watch may be needed this
afternoon, within the next few hours.

..Leitman/Hart.. 07/22/2020

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

ATTN...WFO...GYX...BOX...OKX...ALY...PHI...BGM...CTP...

LAT...LON   40347571 41117585 41827548 42537507 43087463 43367398
            43227301 42787239 42007205 41797217 41437235 40797273
            40587307 40237346 39777424 39807486 40207544 40347571

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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.