The transition will start Wednesday, Sept. 9, as temperatures rise and moisture increases. The National Weather Service says a frontal system will bring thunderstorms from the Midwest into parts of interior New England by Wednesday night.
In central New York and northeast Pennsylvania, the front could trigger scattered showers and thunderstorms beginning late Wednesday afternoon and continuing into the evening. Some storms could produce strong to damaging winds, according to the National Weather Service.
Farther south and east, the main window for showers and thunderstorms will come Thursday, Sept. 10.
The NWS Weather Prediction Center says a cold front moving east will combine with a strong upper-level disturbance and increasingly moist air to produce numerous showers and thunderstorms Thursday afternoon and evening.
The greatest heavy-rain concern is expected across portions of the central Appalachians and upper Ohio Valley, including parts of Pennsylvania and areas just to the west of Virginia and Maryland.
The Weather Prediction Center has placed portions of that region under a Slight Risk for excessive rainfall Thursday. Tropical moisture flowing northward ahead of the front could allow thunderstorms to produce locally heavy downpours.
Forecasters say the setup could also allow storms to repeatedly move across some of the same locations, increasing the risk of isolated flooding.
Northern New York faces an earlier heavy-rain threat. The Weather Prediction Center has identified a Marginal Risk for excessive rainfall as the front moves through Wednesday into early Thursday.
The system should remain progressive, limiting the potential for more widespread flooding there.
Behind the front, cooler and less humid air will begin spreading across the Northeast late in the week, setting up a more comfortable start to the weekend.
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