Two blocks up King Street in Old Town, Alexandria, there is as much as six inches of standing water.
Update: The National Weather Service has upgraded the flash flood watch to a flash flood warning for D.C., Montgomery County and Northern Virginia through 2:30 p.m.
Original story: A large storm system that began late Tuesday will work its way through the D.C. region today, bringing heavy rains, hail, strong winds, and flooding.
The National Weather Service has issued a flash flood watch for most of the area, from Prince William County in Virginia up through northern Baltimore. As much as an inch of rain has already fallen, and up to 4 inches of additional precipitation is expected through tonight.
The steel barriers along the Georgetown waterfront have been raised in anticipation of flooding in the Potomac. In low-lying areas of Old Town Alexandria, as much as six inches of standing water creeping as far as two blocks up King Street.
On the Eastern Shore, heavy rainfall, thunderstorms and gusty winds are possible into Wednesday.
The National Weather Service reminds drivers to avoid driving into standing water, saying "turn around, don't drown."