Washington (CNN) -- A severe thunderstorm packing high winds blew through the Washington metro area Sunday afternoon, downing trees and power lines, and leaving tens of thousands of residents without power.

The storms claimed the lives of two people.

Electricity provider Pepco reported that as of Sunday evening, about 280,000 residences across the District of Columbia, Maryland and Virginia were still in the dark -- and without air-conditioning -- on one of the hottest days of the year, with temperatures reaching 99 degrees at Ronald Reagan Washington National Airport.

"The AC is not running, the stove is not working, the refrigerator is running, and I'm able to plug a fan in," said Leah Schklar, who lives in southeast Washington. "But nothing else is working."

Kerry Heidcamp in the Washington suburb of North Kensington, Maryland, said she was doing what she could to keep cool.

"My house has tiled floors, so I've been laying on the tiled floor because it's actually cold," she said.

Several trees were blocking roads in the district, and live power lines were creating potential hazards, according to the D.C. Homeland Security and Emergency Management Agency. The agency was urging motorists and pedestrians traveling around the city to use caution.

The storm was part of a slow-moving front that struck parts of the Northeast before moving south.

One person was killed and another injured in Beltsville, Maryland, when a tree fell on the car in which they were riding, according to Cpl. Clinton Copeland, a spokesman for the Prince George's County Police Department. The injured person's condition was unknown Sunday night.

One person was killed in Millersburg, Pennsylvania, after being electrocuted by a downed power line, according to the National Weather Service.

The system was expected to continue moving toward the Southeast Monday, but the severe weather threat was expected to expire Sunday night.

CNN's Angela Fritz and Jonathan Helman, and CNNRadio's Matt Cherry contributed to this report.