The extreme rain event starts today — flash flooding and strong wind gusts are likely

This post will be updated through the event.

A long duration, heavy rain event is bearing down on the D.C. region. Slow-moving showers and thunderstorms got an early start on Friday in the Beltway and southern Montgomery County. Flash flood warnings have already been posted and more are possible in the coming hours.

It will probably not rain continuously and some areas will get hit harder than others. But anyone with outdoor plans Friday afternoon through Saturday evening should begin thinking about a Plan B.

Rainfall totals will range from 2 to 4 inches, though it’s possible isolated areas could see around 6 inches when this is all said and done. We’re also seeing the chance of intense wind gusts, which could lead to power outages.

Timeline

The worst of the rain looks like it will come through between 5 p.m. tonight and 5 a.m. Saturday. It’s starting to look more likely that rain will steadily taper off Saturday afternoon, but showers are still possible into Saturday evening.

  • Friday afternoon and evening: Widespread, slow-moving showers and storms develop, likely to produce very heavy rain.
  • Friday night: Waves of thunderstorms with heavy downpours. This will be the worst of it.
  • Saturday: Windy with periods of rain, possibly heavy at times. Rain should taper off through the afternoon.
  • Saturday night: Windy with intermittent showers possible — especially east and northeast of Washington.
  • Sunday morning: Rain should be over, becoming partly sunny and breezy.

Forecast rain amounts through Sunday morning

 

  • National Weather Service: 2 to 4 inches (3.8 inches in Washington)
  • GFS model: 2 to 5 inches (3.3 inches in Washington)
  • NAM model: 1 to 7 inches (4.2 inches in Washington)
  • Canadian model: 2 to 4 inches (4.3 inches in Washington)
  • European model: 1 to 5 inches (1.6 inches in Washington)
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This is a very unusual storm system to develop in late July — in some ways resembling a winter Nor’easter. But because it is the middle of summer and the air is much more humid, this storm system will be able to generate significantly more precipitation than a winter storm.

Heavy storms may line up along a corridor and hit the same areas repeatedly — a worrisome phenomenon known as training. Areas that experience training will be most prone to flooding.

On Thursday afternoon, National Weather Service issued a flash flood watch for the region between Friday afternoon and Saturday afternoon, noting the potential for three or more inches of rain. We expect flash flooding will occur in the areas that get the heaviest rain.

Jason Samenow, Wes Junker and Jeff Halverson contributed to this report.

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