The flash flood watch is in effect from to 1 p.m. Thursday to 2 a.m. Friday in Baltimore, Carroll, Frederick, Harford, Howard and Montgomery counties plus the District of Columbia and parts of Virginia. Cecil County is under a flash flood watch from 8 a.m. Thursday to noon Friday.
Thunderstorms late Thursday afternoon and evening may cause torrential downpours that could lead to flash flooding in the watch areas, the weather service reported.
Rain may fall at a rate of 2 inches per hour, causing a rapid rise in water in low-lying areas; officials remind drivers if they see standing water to turn around—don't drown.
Damaging wind gusts and large hail are possible as well, the weather service reported.
A small craft advisory is in effect on the Maryland portions of the Chesapeake Bay and lower tidal Potomac River, according to the weather service.