Mesoscale Discussion 1945

Issued

Nov 13, 2021, 12:07 PM EST (17:07 UTC)

Expired

Nov 13, 2021, 2:00 PM EST

In force

113 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch likely

Chance of a watch

80%

The Brookhaven radar (KOKX), 57 km from the middle of the area, began a volume at 17:09 UTC, the scan nearest the moment this went out.

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• Severe Thunderstorm Watch 549Nov 13, 12:25 PM EST

921 
ACUS11 KWNS 131707
SWOMCD
SPC MCD 131707 
MAZ000-RIZ000-CTZ000-NYZ000-NJZ000-PAZ000-131900-

Mesoscale Discussion 1945
NWS Storm Prediction Center Norman OK
1107 AM CST Sat Nov 13 2021

Areas affected...Parts of New Jersey...southeastern New York...Long
Island...Connecticut...Rhode Island and Massachusetts

Concerning...Severe potential...Watch likely 

Valid 131707Z - 131900Z

Probability of Watch Issuance...80 percent

SUMMARY...Showers and thunderstorms are expected to intensify across
the region, spreading from near northern Mid Atlantic coastal areas
into southern New England, accompanied by increasing risk for
potentially damaging wind gusts and perhaps a couple of tornadoes
through late afternoon.

DISCUSSION...Although details differ considerably among the various
models, it seems probable that surface low pressure will begin to
consolidate across parts of central New Jersey into the western Long
Island vicinity by mid afternoon, before deepening while continuing
to track east-northeastward across southeastern New England through
22-00Z.  This is expected in response to strengthening large-scale
forcing for ascent, ahead of a vigorous short wave trough currently
pivoting across the northern Virginia/central Maryland vicinity.

It appears that this will include intensifying lift within a
corridor along and ahead of an associated cold front, preceded by at
least weak destabilization within an expanding warm sector across
parts of southeastern New England.  It is uncertain whether
destabilization will be sufficient to support discrete storm
development ahead of the east-northeastward surging cold front, but
the evolution of at least a narrow line of low-topped convection
seems probable in response to the enhanced mesoscale lift.

Likely located along/just north of a belt of 70-90+ kt flow around
the 500 mb level, cloud bearing layer shear will be quite strong and
more than sufficient to contribute to organized convection with the
potential to produce small hail and potentially damaging wind gusts.
 Low-level wind fields are initially relatively modest, with
pre-frontal southerly 850 mb flow still around 30 kt, and this could
slow the development of increasing potential for severe wind gusts. 
However, guidance generally indicates that substantive further
strengthening of this flow to 40-50+ kt is possible, particularly by
late afternoon across parts of eastern Long Island into southeastern
New England, where enlarging low-level hodographs might become
conducive to a risk for tornadoes, in addition to increasing
potential for severe wind gusts.

..Kerr/Hart.. 11/13/2021

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

ATTN...WFO...BOX...OKX...ALY...PHI...

LAT...LON   40777469 41367455 42337294 42307120 40817136 39797396
            39907475 40777469

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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.