Pepco has promised to restore power to 90 percent of the customers who lost it as a result of Friday night's storms by Friday, July 6, at 11 p.m., but tens of thousands of customers may not see their electricity return until even later.

As of 1 p.m. Sunday afternoon, more than 345,000 Pepco customers in Montgomery County, Prince George's County and the District were still without power, the company reported.

At a press conference Sunday afternoon, Pepco Region President Thomas Graham said the company is bringing in resources from across the United States and Canada to help restore power as quickly as possible. But he emphasized that the storm the Washington region experienced -- known as a derecho for its straight-line winds -- delivered a blow worse than some of the hurricanes that have swept through the area in recent years.

"Our system has experienced extraordinary damage," Graham said. "I can think of only one or two occasions where the damage has been greater."

And as bad as things stand now, they would be worse if not for Pepco's efforts to trim foliage around power lines, said Pepco Vice President for Asset Management Michael Maxwell.