Mesoscale Discussion 1946

Issued

Nov 13, 2021, 2:06 PM EST (19:06 UTC)

Expired

Nov 13, 2021, 3:30 PM EST

In force

84 min

Issued by

the Storm Prediction Center

Concerning

Severe thunderstorm watch 549

Counties Hampden County, MA, Worcester County, MA, Nassau County, NY, Suffolk County, NY, Providence County, RI

The Brookhaven radar (KOKX), 61 km from the middle of the area, began a volume at 19:08 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.

804 
ACUS11 KWNS 131906
SWOMCD
SPC MCD 131906 
MAZ000-RIZ000-CTZ000-NYZ000-132030-

Mesoscale Discussion 1946
NWS Storm Prediction Center Norman OK
0106 PM CST Sat Nov 13 2021

Areas affected...Parts of central into eastern
Massachusetts...Connecticut...Rhode Island...and Long Island

Concerning...Severe Thunderstorm Watch 549...

Valid 131906Z - 132030Z

The severe weather threat for Severe Thunderstorm Watch 549
continues.

SUMMARY...The risk for potentially damaging wind gusts seems likely
to increase through 3-5 PM EST, in association with an eastward
advancing band of showers and thunderstorms across Long Island and
Connecticut into parts of central and eastern Massachusetts and
Rhode Island.

DISCUSSION...Pre-frontal boundary-layer destabilization remains
largely driven by steepening low-level lapse rates due to insolation
and mixing.  Due to the mixing, surface dew points actually have
fallen a couple of degrees across most areas, and range from the mid
30s to mid 40s F across all but Long Island into far southern
Connecticut, where they are near 50F.  Still, the eastward
progression of mid-level cooling due to cold advection and lift
should be sufficient to maintain the narrow band of low-topped
thunderstorms focused along and to the northwest of the 100+ kt
southwesterly offshore 500 mb speed maximum.

Two hourly surface pressure falls on the order of 3-4 mb were
evident in 18Z observations along a corridor from the New Jersey
coast through the Concord, NH vicinity, and are likely to be
accompanied by strengthening of southerly low-level flow during the
next few hours.  The latest Rapid Refresh suggests that this may
include speeds in excess of 40 kt around the 850 mb level across
eastern Long Island into eastern Massachusetts by 21-22Z.  Coupled
with further steepening of low-level lapse, downward mixing of
higher momentum probably will contribute to increasing risk for
potentially damaging wind gusts.

..Kerr.. 11/13/2021

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

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

LAT...LON   42637232 42167140 40877193 40557281 40067391 40547384
            41277321 41927287 42637232

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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.