Strong thunderstorms swept across much of the Washington region Thursday afternoon, producing a lightning strike that injured an air traffic controller, stopping all arrivals and departures at Baltimore-Washington International Marshall Airport for more than two hours and knocking out power to thousands.

The storms’ largest impact appeared to be at the region’s three airports, where flights were delayed at Reagan National and Dulles International.

BWI stopped all flights about 2:30 p.m. after the report of a lightning strike, said Jonathan Dean, an airport spokesman. The airport reopened about 4:45 p.m., with two runways closed.

John Dunkerly, president of the National Air Traffic Controllers Association, told the Associated Press he had just left the tower when lightning struck a runway.

Dunkerly said a traffic coordinator who was turning on equipment was shocked when electricity traveled to the tower. A Federal Aviation Administration official said the worker, who went to the hospital, did not appear to be seriously hurt, the AP reported.

Updates of power outages starting at 2 p.m. on Sept. 12, 2013, during the severe weather in the D.C. area. Roll over chart for detailed outage figures.

Ground transportation appeared to fare better, but flooding slowed traffic on roads in the District, Montgomery County and elsewhere. D.C. police briefly closed two blocks of Virginia Avenue NW in Foggy Bottom when standing water covered the street.

In Montgomery, officials received reports of trees down in Rockville and Potomac, along with minor flooding throughout the county, including River Road and Bradley Boulevard.

At the height of the storms, Pepco reported as many as 17,000 power outages, including 13,000 in Montgomery, primarily in areas near Germantown. As of 9 p.m., 3,200 Pepco customers remained without services, along with 1,700 BGE customers. In Northern Virginia, Dominion had only 200 customers in the dark.

The storms were ushered in by a strong cold front. The good news should arrive Friday, with partly sunny skies, gusts of near 30 mph, and highs in the mid- to upper 70s.

Jason Samenow contributed to this report.