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ACUS11 KWNS 220908
SWOMCD
SPC MCD 220908
RIZ000-NYZ000-221145-

Mesoscale Discussion 1130
NWS Storm Prediction Center Norman OK
0408 AM CDT Sun Jul 22 2018

Areas affected...Eastern Long Island to Block Island

Concerning...Severe potential...Watch unlikely

Valid 220908Z - 221145Z

Probability of Watch Issuance...5 percent

SUMMARY...A marginal risk for a brief tornado threat exists across
mainly eastern Long Island, New York to Block Island, Rhode Island
through the early morning. This threat could be a brief tornado
forming over land or a waterspout moving inland.

DISCUSSION...Trends in surface analyses indicated the western
portion of a warm front had advanced into western Long Island where
surface dew points were in the lower 70s F south of this boundary.
This boundary extended to the east-southeast, south of eastern Long
Island. Modifying the 00Z OKX sounding, warmer surface
temperatures/dew points in the lower 70s F (i.e. those that are
found in the warm sector) are needed to weaken inhibition for
convection to realize surface-based parcels/weak instability.
Meanwhile, mosaic radar imagery showed a 40-50 mile wide corridor of
showers and embedded storms extending from eastern Long Island to
approximately 180 miles east/southeast of ACY, with this activity
attendant to a confluence zone, which was moving slowly to the east,
while individual cells were tracking to the north/northwest. Radar
imagery has been indicating periodic, weak low-level rotational
couplets embedded in this convective band, and the OKX VAD modified
with a storm motion of 35-40 kt to the north-northwest results in
0-2-km and 0-3-km SRH around 300 m2/s2. The favorable low-level
shear environment will support additional low-level rotational
couplets with a brief tornado threat as storms encounter the slow northward-moving warm front, where shear should be enhanced, and
then weaken north of the front. Overall weak instability will limit
both the coverage of this severe-weather threat and the need for a
watch.

..Peters/Edwards.. 07/22/2018

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

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

LAT...LON 40687303 41037299 41197235 41217195 41287152 41177128
40957139 40637287 40687303



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