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Outlook for Sunday, September 25

Outlook Summary

Widely scattered strong thunderstorms posing at least some risk for damaging wind gusts and hail remain possible across the the Allegheny Plateau into northern Mid Atlantic and southern New England coast vicinity through early this evening.

Outlook Images

overview

tornado 2%

wind 15%

hail 5%

Detailed Outlook

SPC AC 251932

Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0232 PM CDT Sun Sep 25 2022

Valid 252000Z - 261200Z

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS INTO EARLY EVENING ACROSS PARTS OF THE NORTHERN MID ATLANTIC INTO SOUTHERN NEW ENGLAND

### SUMMARY

Widely scattered strong thunderstorms posing at least some risk for damaging wind gusts and hail remain possible across the the Allegheny Plateau into northern Mid Atlantic and southern New England coast vicinity through early this evening.

20Z Update

Stronger mid-level wind fields (in the 700-500 mb layer) associated with a lead short wave perturbation now appear generally east of the Allegheny Mountains, and are expected to shift across the northern Mid Atlantic coast through early evening. A band of convection, which appears supported by the stronger mid/upper forcing for ascent, may be outpacing the more substantive (albeit modest to weak) boundary-layer destabilization to the east of the Alleghenies, and appreciable further intensification seems unlikely. However, widely scattered thunderstorm development remains possible late this afternoon, in the presence of strongly sheared, 40-50+ kt deep-layer westerly mean flow across the Allegheny Plateau into northern Mid Atlantic and southern New England.

..Kerr.. 09/25/2022

.PREV DISCUSSION… /ISSUED 1120 AM CDT Sun Sep 25 2022/

Mid-Atlantic and vicinity through this evening

A midlevel shortwave trough over the upper OH Valley will eject eastward toward the Mid-Atlantic and southern New England, in response to an upstream shortwave trough digging south-southeastward from MB toward the upper MS Valley. Some deepening of a surface cyclone is expected in the vicinity of the lower Great Lakes in association with the ejecting midlevel trough, and a weak cold front will progress eastward across the Appalachians by this afternoon to the south of the deepening cyclone. The cyclone warm sector will not be particularly warm or moist, but a narrow zone of cloud breaks from southern PA into WV should allow surface temperatures to warm into the 70s with dewpoints in the mid 50s to near 60. The warming surface temperatures and notable midlevel cooling/steepening of low-midlevel lapse rates (observed at ILN from 00 to 12z) will boost MLCAPE into the 500-1000 J/kg range in a narrow zone immediately ahead of the weak cold front this afternoon.

The specific location and evolution of the main severe threat is a bit uncertain given the presence of clouds and early convection, with the potential for the stronger storms to evolve from the leading edge of the ongoing convection in PA/WV, and farther west within the band of ascent. The weak buoyancy and steepening low-level lapse rates will combine with strengthening midlevel winds to provide an environment favorable for damaging winds with fast-moving, low-topped clusters/bands of convection spreading eastward toward the Mid-Atlantic coast through late afternoon/evening. Isolated large hail may also occur with any stronger storms/supercells given the long hodographs and cool midlevel temperatures, and low-level shear will be strong enough to support a low-end threat for a tornado or two.

Southern Appalachians this afternoon

The southern fringe of the OH Valley midlevel trough will move over the southern Appalachians this afternoon, along with the remnant monsoonal moisture plume. Clouds/ongoing convection will tend to disrupt surface heating across northern AL/GA and southeast TN, and the southern fringe of the somewhat stronger forcing for ascent with the OH Valley trough is expected to pass over eastern KY/WV/VA. Thus, with modest buoyancy and the aforementioned concerns, storm coverage into the southern Appalachians is uncertain. Where storms form with afternoon heating in cloud breaks, there will be the potential for isolated damaging gusts and marginally severe hail.

WI/southwest Lower MI this afternoon into early tonight

The shortwave trough now approaching northern MN will reach WI later this afternoon/evening, and then continue southeastward to Lower MI tonight. Cooling midlevel temperatures, residual low-level moisture, and surface heating in cloud breaks will support the potential for low-topped thunderstorm development by mid-late afternoon across WI. Lapse rates will be sufficiently steep and midlevel flow sufficiently strong for a low-end threat for wind damage. Despite arrival after the diurnal cycle, the threat for isolated wind damage could persist across Lake MI into southwest Lower MI, where the relatively warm lake will help maintain weak buoyancy and low-level lapse rates after sunset.

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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z

National Risk Overview

Sunday, September 25
TORNADO: 2%
HAIL: 5%
WIND: 15%
Monday, September 26
TORNADO: 2%
HAIL: low
WIND: 5%
Tuesday, September 27
ANY SEVERE: 5%
Wednesday, September 28
ANY SEVERE: low / uncertain
Thursday, September 29
ANY SEVERE: low / uncertain
Friday, September 30
ANY SEVERE: low / uncertain
Saturday, October 1
ANY SEVERE: low / uncertain
Sunday, October 2
ANY SEVERE: low / uncertain

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