More than 1 million homes and businesses in a swath from Indiana to Virginia remained without power on Wednesday, five days after deadly storms tore through the region.
The outage meant no July 4 Independence Day holiday for thousands of utility workers who scrambled to restore lingering power outages.
Much of the damage to the power grid was blamed on last weekend's rare "derecho," a big, powerful and long-lasting wind storm that blew from the Midwest to the Atlantic Ocean.
Violent weekend storms and days of record heat have killed at least 23 people in the United States since Friday. Some died when trees fell on their homes and cars, and heat stroke killed others.
Energy provider Dominion Virginia Power said emergency crews were working around the clock to deal with 60,000 outages for its customers throughout Virginia as of noon Wednesday.
Service for virtually all customers in Northern Virginia and the Richmond metropolitan area who lost electric service because of the storms should be restored by Friday night, said Daisy Pridgen, a Dominion spokeswoman. In a few instances, work may continue into Saturday where there was extreme damage, she said.
More than 5,000 people from 18 states and Canada were working through the holiday, Rodney Blevins, a Dominion vice president, said in a statement. The company said it had restored power to about 90 percent of its 1 million customers who had lost electric service because of the weekend storms, the biggest non-hurricane outage in the company's history.
Much of the hardest-hit areas were to bake for another day in scorching heat, with the National Weather Service forecasting temperatures from 90 Fahrenheit (32 Celsius) to more than 100 F (37.7 C) from the Midwest to the Atlantic Coast.
In Washington, about 5,000 customers of local power company Pepco were still without power on Wednesday morning, and the city was distributing food to people who were unable to cook at home. Closer to 50,000 Pepco customers in suburban Maryland were still in the dark.
But the region still most affected, however, was West Virginia and the neighboring Blue Ridge Mountain section of Virginia, accounting for close to half of the lingering outage.
In West Virginia, 174,960 of Appalachian Power's half-million customers remain without electric service, the company said in a noon update on Wednesday.
Just over the state line in the mountains of western Virginia, 110,578 Appalachian clients remained blacked out, it said.
"Crews are continuing to find additional damage to our distribution and transmission facitilities," a statement on the company's website said. It said additional crews from outside the area will join restoration efforts as they become available.
More than 3,000 workers are dedicated to its effort in Virginia and West Virginia, the company said. Other utilities also pledged to keep crews working - some in 16-hour shifts - until the electricity was restored.
Virginia's Arlington County, across the Potomac River from Washington, still had 6,875 people without power as of 7 a.m, said John Crawford, deputy director of the county's office of emergency management.
Verizon services to the county's 911 emergency communications center are "still not 100 percent stable," but have been up and running for 48 hours without known incident, he told Reuters.