Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
321 PM EDT Wed Sep 22 2021

Valid 00Z Thu Sep 23 2021 - 00Z Sat Sep 25 2021

...Widespread heavy rain, localized severe weather to transpire with areas
of flooding likely from the Great Lakes to the northern Mid-Atlantic this
evening; Moderate Risks for Excessive Rainfall are posted...

...Swath of heavy showers and thunderstorms reaches the Northeast on
Thursday; hazards such as flash flooding and severe weather are possible...

...Autumn-like temperatures in the South and Northern Plains; the West
Coast gradually warms up the second half of the week...

All eyes are on a strengthening area of low pressure located in the Ohio
Valley this afternoon. This storm system is intensifying thanks to a
deepening upper level low tracking through the Lower Great Lakes region.
This wave of low pressure is responsible for ongoing showers and
thunderstorms up and down the East Coast and as far west as the eastern
Corn Belt. Thunderstorms will be severe at times from the Ohio Valley on
south into the Carolinas with damaging wind gusts, large hail, and
tornadoes all possible. In addition, a rich feed of tropical moisture
accompanied within a robust southerly wind field aloft supports Excessive
Rainfall rates within heavy showers and thunderstorms in advance of, and
along, an advancing cold front. This has led to the issuance of two
Moderate Risks for Excessive Rainfall; one in the central Appalachians and
one in portions of the Lower Great Lakes. Heavy rainfall rates leading to
areas of flash flooding is also a concern in the northern Mid-Atlantic
where soil moisture anomalies remain overly saturated versus normal for
parts of the region. This has resulted in Flash Flood Watches being issued
in these aforementioned areas, including for some of the major markets of
the northern Mid-Atlantic. On the back side of the storm, periods of
moderate-to-heavy rainfall is likely to produce areas of flash flooding in
the lower Great Lakes this evening. Rapid runoff, fast rising creeks and
streams, and urbanized flash flooding are all expected to occur where the
most intense rainfall rates take shape.

As the low occludes over the Great Lakes tonight and into Thursday, the
cold front will gradually push east, shifting the focus for heavier
rainfall into the Northeast on Thursday. A Slight Risk for Excessive
Rainfall remains in place from the northern DelMarVa Peninsula and
Delaware Valley on north into the interior Northeast. The front's slow
progression will keep rounds of heavy showers and thunderstorms in the
forecast across much of New England on Friday, where a Marginal Risk for
Excessive Rainfall is in place. Farther south, the trailing end of the
cold front comes to a crawling speed over central Florida, leading to
daily rounds of strong thunderstorms capable of producing locally heavy
downpours over South Florida both Thursday and Friday.

Behind the front, high pressure and dry conditions look to stick around
throughout the Nation's Heartland Thursday and into Friday. Farther west,
a relatively dry cold front brings a reinforcing shot of autumn-like
temperatures to parts of the northern Rockies on Thursday, then into the
Northern Plains on Friday. Seasonally cooler temperatures and more
refreshing humidity levels engulf much of the South, while the West Coast
heats up as a ridge of high pressure aloft builds in by Friday.

Mullinax

Graphics are available at www.wpc.ncep.noaa.gov/basicwx/basicwx ndfd.php