The storm caused power outages from Indiana to New Jersey and was blamed for the deaths of at least 13 people, including at least six in Virginia; two in New Jersey; two in Maryland; one in Ohio; and one in Washington, D.C.
Among the deaths were two people in Springfield, Va. -- a 90-year-old woman who was killed in her bed after a tree fell on her home, and Khiet Nguyen, 27, whose car was hit by a falling tree as he was driving, police said. He was pronounced dead at the scene.
"We have six confirmed fatalities, because of the storms last night, we have about a million customers without power, within Virginia and obviously we're looking at extremely high temperatures today, and that's our big concern," Virginia Department of Emergency Management spokesman Bob Spieldenner said.
The storm also stranded 232 people on an Amtrak train in West Virginia, when the rail line was blocked on both sides by trees that fell on the tracks.
The passengers finally got off the train Saturday evening and were put on buses that would follow the route of the train and take them to the train station in Cincinnati, Ohio.
The storm raced across 12 states and brought tremendous downpours, lightning and wind gusts that topped 90 mph in some spots.
Spanning 700 miles, this long line of thunderstorms is called a "derecho." "Derechos" plow everything in their path and are characterized by a long line of wind gusts of at least 60 mph.
West Virginia Gov. Earl Ray Tomblin declared a state of emergency after half a million residents were left without power. The state has set up cooling shelters for its residents.
Jimmy Gianato, the director of the Homeland Security and Emergency Management Department in West Virginia, urged residents to check on their neighbors with triple digit temperatures expected again today.
"Our greatest concern is the pending heat wave that's to be here ... with 102 degree temperatures. We're looking at the contingencies we need to make tonight to make sure that we can take care of our citizens tomorrow," he said Friday night.
Paul Howard, director of operations at the West Virginia Division of Homeland Security and Emergency Management, said there are "in the neighborhood of 600,000 to 700,000 customers" without power in the state.
The storms left two-thirds of Ohio without power, and a state of emergency has been declared as stifling heat is in the forecast for today.
"We know the temperatures are going to climb," said Tamara McBride of Ohio's Emergency Management Agency. "So, recognizing that power outages are the factor at this point, we're working with local communities to identify cooling shelters that either have back-up generators or areas that did not lose power."
Nearly 300,000 residents were without power in the state.
Washington, D.C., also felt the brunt of the storm. After a day of intense heat, 400,000 people were reported to have lost power.
"We have more than half our system down," Pepco spokeswoman Myra Oppel told The Associated Press. "This is definitely going to be a multi-day outage."
Twenty states are under some kind of heat warning or advisory today, mostly from the Mid-Atlantic through the south and into parts of the Midwest.