Sluggish Storm Finally On The Move As It Spreads Localized Flood Threat To Mid-Atlantic

More Heavy Rain Expected For Mid-Atlantic

A slow-moving storm system that has soaked the South for days is finally beginning to move, spreading its heaviest rain and possible localized flood threat into parts of the East Tuesday.

Forecast

Scattered showers and thunderstorms will linger over the Southeast today, but the greatest chance of localized flooding will shift north into the mid-Atlantic and the adjacent Appalachians. That includes parts of the Washington, D.C. metro and Richmond and Norfolk, Virginia.

Flood watches have been issued by the National Weather Service for today from parts of North Carolina to Virginia, western Maryland and south-central Pennsylvania. This means flooding is possible in these areas where too much rain falls too quickly, even though some locations are in drought.

A few isolated severe storms are also possible, which could produce damaging wind gusts or an isolated tornado.

Below is a look at the latest radar along with any active watches and/or warnings issued by the National Weather Service.

After today, the chance of localized flooding will trend downward. But, pockets of rainfall will persist in the East Wednesday as the storm system finally begins to exit.

Why So Stubbornly Wet?

First, an area of low pressure in the Southeast is being blocked by high pressure to the north. That means it will move very slowly, and slow-moving lows mean slow-moving areas of precipitation.

Second, this Southeast low is tapping a plume of deep moisture known as an atmospheric river.

You may have heard this term used for Pacific storms hammering the West Coast, but they occur around the world, including in the eastern United States.

By Tuesday, this atmospheric river plume could be almost 2,000 miles long from Central America to the mid-Atlantic states.

Atmospheric rivers can wring out heavy rain due to their incredible moisture content. One study estimated that the moisture flux is roughly equal to that of the Amazon River – about 176,000 tons per second.

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. Extreme and bizarre weather are his favorite topics. Reach out to him on Bluesky, X (formerly Twitter) and Facebook.