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Posted at 06:15 PM ET, 09/30/2010

Second wave of heavy rains advancing north

Another 1" or more possible, DC and east

* Flash Flood Warning extended until 12:15 a.m. *
* Storm impact coverage: PostLocal | Live chat transcript *
* Flash Flood Watch thru tonight | Share photos | Dr. Gridlock *
* Citizen observer rain totals: VA, MD | NWS Mesonet rain totals *
* Outside now? Radar, temperatures & more: Weather Wall *

This isn't over.

Another large area of rain extending southeast through North Carolina and into the Atlantic ocean is headed north and taking aim at the metro region. Rain, sometimes quite heavy (especially from DC and to the east), will again overspread the metro region over the next several hours. Flash flood warnings have been reissued where they were discontinued and extended until 12:15 a.m. for the entire metro region.

Based on current radar trends and model guidance, it looks like another inch or two could fall inside the beltway, around 1" in the north and west suburbs (with amounts decreasing sharply north and west of eastern Loudoun and Montgomery counties) and 1-3" in the eastern suburbs. This rain will be on top of the 2-5" (and isolated 5-9" amounts) which fell earlier today. As was the case this morning, some localized amounts may well be above the "average".

If you are out and about this evening, it is especially important not to attempt to drive through flooded roadways given limited nighttime visibility.

Keep reading for more on this evening's rain threat...

There is a fair amount of uncertainty in the exact rainfall amounts because of a sharp western cutoff with the current batch of rain. As the National Weather Service describes in its afternoon discussion:

LATEST MODEL GUIDANCE CONTINUES TO SHOW ANOTHER WAVE OF LOW PRESSURE MOVING UP THE MID-ATLANTIC COAST THIS EVENING INTO THE OVERNIGHT HOURS. THERE WILL BE A SHARP WESTERN CUTOFF BETWEEN LIGHT PRECIP AND ANOTHER BAND OF HEAVY PRECIP. THEREFORE...ANY SLIGHT SHIFT BETWEEN THE BACK EDGE OF PRECIP WILL MAKE A HUGE DIFFERENCE WITH ADDITIONAL PRECIP ACCUMULATIONS TONIGT. CURRENT THINKING IS THE WESTERN SHORE [OF CHESAPEAKE BAY] IS UNDER THE GUN AGAIN WITH AN ADDITIONAL 1-3 INCHES POSSIBLE WITH THIS ACTIVITY... WHILE AREAS FARTHER TO THE WEST WILL RECEIVE MUCH LESS.

The rain should end in the early morning hours from southwest to northeast. Refer to Ian's PM Update for additional information on Friday's forecast.

By  |  06:15 PM ET, 09/30/2010

Categories:  Floods, Floods

 
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