A fast-moving line of thunderstorms downed trees and power lines across the northern and western sections of the Washington area last night, leaving thousands of homes without power. A spokeswoman said some outages in Northern Virginia could persist until this afternoon.

Nearly 15,000 customers of Dominion Power were without electricity late last night as lightning blew fuses and toppled trees onto power lines, company spokeswoman Le-Ha Anderson said. Crews had more than 250 trouble spots to tend to and were unable to begin repairs in many areas because a second band of storms was crossing the area, she said.

The storms earlier in the evening produced frequent lightning and wind gusts of almost 40 mph at area airports, and hail was reported in Loudoun County, the National Weather Service reported.

In Montgomery County, a lightning strike started a roof fire in Potomac, and county police and fire officials reported felled trees and wires in areas including Germantown, Bethesda and Rockville. No one was injured in the fire.

According to Pepco, about 10,000 customers lost power, with about 8,500 of them in Montgomery. By 10:45 p.m., power had been restored to all but 4,500 of those homes. In Northern Virginia, most outages were in Arlington, Alexandria, McLean and Springfield, Anderson said.

Forecasters predict a 30 percent chance of showers and thunderstorms this afternoon and evening.

Lightning streaks over Route 1 in Hyattsville. Outages in Northern Virginia could continue into this afternoon.