The eastern third of the United States braced for more scorching temperatures on Tuesday as nearly 1.4 million homes and businesses from Illinois to Virginia remained without power heading into Independence Day holiday.
Violent weekend storms and days of oppressive heat have killed at least 18 people in the United States. Some died when trees fell on their homes and cars, while heat stroke killed others.
Utilities warned that some people could be without power - and unable to run their air conditioners - for the rest of the week. In all, more than 1.4 million homes and businesses from Illinois to Virginia remained without electricity on Tuesday morning.
In hard-hit Washington, D.C., Mayor Vincent Gray expressed frustration with the slow pace of repairs. He said the local power company, Pepco, had told him that 90 percent of those without power in the U.S. capital would have it restored by Friday.
"We have had power outage after power outage in the District of Columbia. Frankly, the people are just fed up with it. I don't have any power in my own home," Gray told CNN.
Residents and businesses were also struggling with outages in Virginia, West Virginia, Ohio, Tennessee, Pennsylvania, Maryland, New Jersey, North Carolina, Indiana and Kentucky.
Baltimore Gas and Electric, an Exelon Corp unit, said it had 165,000 customers still without power and restoration was expected to run into the weekend.
"This is an act of God, and this is the way that all utilities around the country work. This is not something that is unique to any part of the country," spokesman Robert Gould said on CNN.
Temperatures from 90 Fahrenheit (32 Celsius) to more than 100 F (37.7 C) were forecast from the plains to the Atlantic Coast on Tuesday and Wednesday, the Fourth of July holiday.
"Over the next few days much of the eastern third of the country will see a resurgence of the heat experienced last weekend," U.S. weather forecasters said.
The record books got a brief respite. On Sunday, 288 temperature records were set nationwide. On Monday, Mechanicsville, Maryland, tied a record high temperature of 94 degrees F (34.4 C), set in 1983, but no heat records were broken, the National Weather Service said.
The upper Midwest could see more severe thunderstorms like the one that ripped down trees and power lines in northern Minnesota and knocked out the phone system in the city of Bemidji and soaking Duluth.
Much of the devastation to the power grid was blamed on last weekend's rare "super derecho," a storm packing hurricane-force winds across a 700-mile (1,100-km) stretch from the Midwest to the Atlantic Ocean.
A derecho - Spanish for "straight" - is a long-lasting wind storm that accompanies fast-moving thunderstorms or showers, AccuWeather said. The most powerful derechos are called "super derechos," described by AccuWeather as a "land hurricane."
With power lines down across the region, the U.S. government told federal workers in the Washington area they could take unscheduled leave or work from home on Monday and Tuesday.
Two of the largest property insurers, USAA and Nationwide, said they had received more than 12,000 claims in total from the weekend storms. Most were for house damage.
The storms capped a costly June for insurers, which were already facing losses of at least $1 billion from a hailstorm that ripped through Dallas.