In places where it rained Friday, it rained again and again, with waves of downpours, accompanied by powerful wind gusts that toppled trees and caused electricity to go out and stay out for hours.

Part of the flat roof of a car dealership in Manassas caved in. Patty Prince, a city spokeswoman, said it was believed to be the result of a clogged drain. She said one employee twisted an ankle in fleeing.

Most of the area’s power outages were in Northern Virginia, inside the Capital Beltway.

About 7,800 Alexandria homes and businesses lacked power late Friday. It was not clear when it would be restored. The work appeared to be slow going.

By late Friday, 2.86 inches of rain had fallen at Reagan National Airport. On the other hand, Dulles International Airport recorded less than a fifth of an inch.