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Day 3 Outlook 0830Z Probablistic 0830Z
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Categorical Day3 0830Z Outlook
  

Images courtesy of the NWS Storm Prediction Center
 Forecast Discussion

    
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ACUS03 KWNS 210701
SWODY3
SPC AC 210700

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0200 AM CDT Tue Sep 21 2021

Valid 231200Z - 241200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THURSDAY ACROSS
PARTS OF SOUTHEASTERN NEW YORK STATE...ADJACENT PORTIONS OF
MASSACHUSETTS...CONNECTICUT...AND LONG ISLAND...MUCH OF NEW
JERSEY...EASTERN PENNSYLVANIA...DELAWARE...MUCH OF CENTRAL AND
EASTERN MARYLAND...THE DISTRICT OF COLUMBIA...EASTERN VIRGINIA AND
NORTHEASTERN NORTH CAROLINA...

...SUMMARY...
Scattered strong thunderstorms may impact parts of the northern Mid
Atlantic region Thursday, accompanied by at least some risk to
produce potentially damaging wind gusts.

...Discussion...
Models indicate that amplification within the westerlies will
continue through this period, with mid-level ridging building across
the Canadian Rockies into the Canadian Prairies, and downstream
troughing digging across the central international border area into
the northern U.S. Great Plains.  In response to these developments,
and as blocking persists in the downstream pattern across the
mid-latitude Atlantic, a significant mid-level low initially over
the lower Ohio Valley is forecast to accelerate north-northeastward,
across and northeast of Lake Huron by 12Z Friday.  

The lead mid-level perturbation will be accompanied by an occluding
surface low, with a trailing cold front advancing east of the lower
Great Lakes and Appalachians, toward the Atlantic coast.  A
significant reinforcing cold front likely will surge southeastward
through much of the northern Great Plains by late Thursday night. 
In the wake of the lead cold front, generally dry and stable
conditions are expected across most areas.  However, some low-level
moisture return through the Gulf of California, beneath a
southwestward propagating pocket of relatively cool mid-level air,
may contribute to widely scattered thunderstorms across parts of the
Southwest.

Ahead of the lead cold front, 30-50+ kt southerly flow in the
850-700 mb layer may linger through much of the day Thursday across
the northern Mid Atlantic.  It appears that this will coincide with
a corridor of seasonably moist air that may develop weak to moderate
CAPE and support scattered thunderstorm development with daytime
heating.  Although lapse rates likely will be generally weak, some
of this activity may be able to organize into lines or clusters,
with precipitation loading contributing to downward momentum
transfer and the potential for locally damaging wind gusts, before
convection weakens Thursday evening.

..Kerr.. 09/21/2021

$$