The storms swept across West Virginia, Virginia, Washington and Maryland, with wind speeds of up to 75mph (120 kph).
The power outages left many without air conditioning after a day of record-breaking 104F (40C) heat.
Authorities were reportedly investigating two deaths linked to the storm.
The storm is locally referred to as a "derecho" - a violent, straight-lined windstorm associated with a fast-moving band of severe thunder storms.
It left behind felled trees, streets littered with fallen branches and downed power lines.
Services on all Washington metro lines was affected, with trains sent to their end points after trees fell across the tracks and power was lost.
The storms started in the Midwest and moved quickly eastward toward the mid-Atlantic states.
The social network site Twitter buzzed with speculation about how long the power cuts would endure, with one user warning: "Check on your neighbors!"
Associated Press quoted police in Springfield, Virginia as saying a woman had died when a tree fell on her home at the height of the storm.
The Washington Post said another death in the same Fairfax County had also been attributed to the storm.
"High temperatures reached record levels in the mid-Atlantic states today [Friday]," said the National Weather Service.
"In fact... new all-time highs for June... and even all-time highs for any year... were established," it said on its website.
It said the heat should become less intense over coming days, but warned that thunder storms and potentially severe weather remained a threat.