Wednesday, 11:35 a.m.
The front extending from Lake Erie to the western Gulf of Mexico has already had a history of excessive rains. Just as the people in central and eastern Texas over the past couple of days. San Antonio picked up over 3 inches of rain, Austin over 4 inches. Houston had 3 to 4 inches of it yesterday, and there's been quite a bit of rain in parts of Tennessee and Arkansas. More will fall this afternoon and tonight. And it won't stop there.
As this front drives eastward across the South tonight, it will begin to slow down, while at the same time, it will only crawl eastward across the Ohio Valley into the Appalachians over the next 36 hours. Look at the NAM model forecast for this afternoon:
Compare that to the Friday morning forecast:
Now, look at the latest infrared satellite image:
We already have a tropical tap from the southern Gulf feeding into the rain and thunderstorms with and ahead of the front from the lower Mississippi Valley and central Gulf Coast region into the Tennessee Valley. Look at the 700mb moisture forecast for early Friday morning:
For all effective purposes, this front will be the convergence of moisture from the Gulf and Caribbean and even from the southwest Atlantic. As this is pooled along the front, and it is forced to move slowly because of the strong upper-level high over the northwest Atlantic, the tropical moisture will merge into a band of very heavy rain with embedded thunderstorms that could yield 3 to 5 inches of rain in some places from the Southeast right up the Appalachians into parts of Pennsylvania and New York. In accordance with that, here's the latest, 84-hour total QPF from the 12z NAM model:
Flooding is thus going to be a major concern the rest of the week, even into Friday night and Saturday in western New England and the Hudson Valley before the frontal rains weaken later Saturday as they slowly advance into eastern New England.
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