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Day 1 Outlook Convective Tornado Hail Wind

Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point. Probability of one inch diameter hail or larger within 25 miles of a point. Hatched Area: 10% or greater probability of two inch diameter hail or larger within 25 miles of a point. Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% or greater probability of wind gusts 65 knots or greater within 25 miles of a point.

  
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ACUS01 KWNS 030600
SWODY1
SPC AC 030559

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1259 AM CDT Wed Jun 03 2020

Valid 031200Z - 041200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF PA INTO NJ AND THE NYC METRO...

...SUMMARY...
Clusters of strong to severe storms are possible today and tonight
from the central Plains through the Midwest and Mid-Atlantic. The
most intense storms, capable of damaging winds and hail, are
expected from parts of Pennsylvania into New Jersey and the New York
City metro area.

...Synopsis...

A broad swath of northwesterly flow will stretch from the northern
High Plains to the Great Lakes and Northeast/Mid-Atlantic today as
several shortwave impulses migrate through northern-stream flow. At
the surface, 60s F dewpoints will exist from the southern/central
Plains eastward across much of the Midwest to the Mid-Atlantic ahead
of a southward sagging cold front. More modest boundary-layer
moisture will exist across the northern/central High Plains a more
diffuse cold front associated with a surface low over Saskatchewan
develops eastward.

...PA into the Mid-Atlantic...

Storms are expected to develop in the vicinity of Lake Erie by late
morning as a cold front develops east/southeast across the
international border. Ahead of the front, low to mid 60s dewpoints
will be maintained on southwesterly low level flow. Seasonally warm
temperatures in the 70s to low 80s will support MLCAPE values from
1500-2000 J/kg. Fast midlevel flow will be in place across the
region with 35-50 kt winds noted in the 850-700 mb layer in most
guidance. Deep layer flow will mainly be unidirectional, but
increasing winds with height from the surface through 700 mb will
result in effective shear greater than 40 kt, supporting organized
storm structures amid moderate midlevel lapse rates (7-7.5 C/km).
Daytime heating will result in steepening low-level lapse rates, and
PW values near 1.75 inches will further support strong downdrafts.
Some upscale growth is expected via outflow interactions and
possible cold pool generation. Most CAMs guidance support one or
more bowing segments tracking east/southeast across portions of
northern/eastern PA into NJ and the NYC Metro area from early
afternoon into the evening hours, and a corridor of damaging winds
is expected. Some severe hail is also possible given the
thermodynamic and kinematic parameter space, but may be limited by
storm mode.

...Midwest...

Thunderstorms are expected to develop in the vicinity of the surface
cold front from MO eastward through OH. Strong heating and
mid-to-upper 60s F dewpoints beneath modestly steep midlevel lapse
rates will support 2000-3000 J/kg MLCAPE. Deep-layer flow will be
weaker across the Midwest as strong shortwave impulses are expected
to remain to the west across parts of the Plains and to the east
across the Mid-Atlantic, and effective shear will be marginal,
around 20-30 kt. This will result in briefly intense cells capable
of strong downburst winds and hail. 

...Portions of the Northern/Central Plains...

A shortwave impulse is forecast to eject across WY and shift
east/southeast over NE/KS toward northwest MO through the period.
Initial high-based convection over the northern High Plains will
pose a threat for strong downburst winds via a dry, deeply-mixed
sub-cloud layer. As the impulse shifts east toward the central
Plains, convection will encounter increasing moisture and a
strengthening low level jet during the evening/overnight. Initial
cells will be capable of large hail with midlevel lapse rates in
excess of 8 C/km and 40+ kt effective shear across the region. By
evening, upscale growth is expected as the low level jet increases,
and a bowing MCS may track eastward across parts of NE and northern
KS, posing a damaging wind threat.

..Leitman/Lyons.. 06/03/2020

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