It may be near the end of the week before power is restored to some of the millions of those lacking electricity following weekend storms as another day of sweltering temperatures was forecast for much of the nation Monday.

The intense early-summer weather has baked areas from Missouri to New York to Georgia with record-breaking heat and unleashed fierce storms that knocked out power over the weekend. At least 16 people were killed from the series of storms.

While the mercury Monday was forecast to stop short of the century mark in many areas, high temperatures will still approach 100 degrees and will definitely be in the 90s for most of the eastern two-thirds of the country, according to CNN meteorologist Sarah Dillingham.

A high of 99 degrees is forecast for Louisville, Kentucky, for instance, and 96 degrees in Columbus, Ohio.

Eighteen states remained under heat advisories, excessive heat watches and warnings, Dillingham said.

“Hot and hotter will continue to be the story from the Plains to the Atlantic Coast the next few days,” the National Weather Service said Monday. “The widespread excessive heat warnings and heat advisories have certainly decreased in coverage, but temperatures will remain well above average across a large portion of the U.S.”

Cities and towns in the Southeast and Midwest have already endured temperatures of more than 100 degrees for days.

Nearly 2 million customers from Indiana through Maryland were dealing without power early Monday after a massive storm late Friday and Saturday that was fueled, in part, by the extreme heat. Each household is a customer — so the number of people affected is well in the millions.

Of those, nearly a million customers were in Virginia, Maryland and Washington.

As of about 6:30 a.m. Monday, outages in the metro Washington area were about 225,000, down from a peak of 443,000, Pepco CEO Jim Rigby told CNN.

“We’ve restored about 45% of the customers, but obviously, we’re not satisfied,” Rigby said. “We have a lot of work to do, and we won’t be satisfied until we have everyone back.”

He said he understands the frustration some people may be experiencing. Crews from as far away as Canada’s New Brunswick have arrived to help, with more expected Monday, he said. “Our foot is on the pedal.”

Federal agencies in the Washington area will remain open Monday, but nonemergency employees have the option to work remotely. Some schools in the Baltimore area were canceled, CNN affiliates reported.

Pepco previously said it would have power restored to 90% of customers by Friday. Rigby said after making significant progress overnight, he believes “we should be able to beat that.”

However, Friday is a long five days away for those without power.

While down from a peak of about 4 million customers without electricity, the number of storm-related outages was still dangerously high given that people were trying to get by without air conditioning or ice.

“It’s the combination of heat and power outages that are hitting people,” said Tamara McBride of the Ohio Emergency Management Agency. She predicted some may not get electricity until “well into the week.”

“We’ve been sleeping in the basement,” said Mark Cohen of Mays Landing, New Jersey, who lost power in the storms. “Yesterday was 95 and really humid. We just finished our basement, luckily. We put an air mattress down there.”

He said the storm caused damage to his property and knocked out power. “It was the scariest thing I’ve ever been through,” he said. “Just to give you an idea, it was somewhere between a movie and a disaster ride at a park.”

More of the heat-fueled storms were possible Monday across the Mid-Atlantic region and the north-central United States, the National Weather Service said.

“As in recent days, the main threats will be damaging winds and large hail,” Dillingham said. Of the 830 preliminary storm reports received by the weather service Sunday afternoon, 523 involved reports of winds of up to 70 and 80 mph across northern Illinois and Indiana, she said.

Outage numbers early Monday included about 450,000 people in Ohio and more than 650,000 in West Virginia.

Extreme heat is the leading cause of weather-related deaths in the United States.

Many without power sought refuge Sunday in air-conditioned public spots.

“It’s so hot,” Jillian Carney, who went to a mall in Huntington, West Virginia, after being without power for 40 hours, told CNN affiliate WCHS-TV. “We came to the mall mostly ’cause you run out of things to do.”

On one Baltimore street, residents on one side have power while homes facing them do not.

“I can’t dislike them, but they’re all nice and cool over there watching their TVs, and I’m not,” a woman on the side lacking power told CNN affiliate WBFF-TV.

But said resident John Bryan on the other side, “Usually, I’ll lose power and they’ll have power. So this time, I have power back first. So it equals out in the end.”

Another bout of storms Sunday afternoon brought some relief to the heat but danger as well.

The National Weather Service reported that a man in Calico, North Carolina, was killed when a shed fell on him as he was trying to store his golf cart.

A few minutes later, in a nearby town, storm-related winds knocked over a tree that fell on a couple in a golf cart, killing them both.

More deaths tied to the weekend storms were reported from Ohio to New Jersey.

Virginia had the highest death toll, at seven, with the state Department of Emergency Management noting the deaths were spread across four counties.

And in New Jersey, 2-year-old and 7-year-old cousins died after a fallen tree crashed on their tent in Parvin State Park, said Larry Ragonese, a spokesman for the state Department of Environmental Protection.

The stubborn, oppressive heat wave can cause serious health problems, with the effects of heat cumulative. The longer you experience it, the more likely you are to have conditions such as heat stroke and dehydration.

“Current indications are that this heat wave may continue for much of the upcoming work week,” the National Weather Service’s St. Louis bureau warned. “Do not wait until the heat wave has lasted for several days. Take action today to protect your health and continue to do so.”

Between June 24 and Saturday 1,928 record-high temperatures were broken or tied nationwide. That number doesn’t include new ones expected from Sunday that aren’t in the National Climatic Data Center’s official count.

But some tried to make the best of the roasting temperatures.

Holly Coons of Nashville decided to bake cookies on the dashboard of her car when it was 107 degrees outside.

“I actually burned my hand when I grabbed the cookie sheet out of the car,” she said. But the cookies were done. Coons said she would have made a larger batch had she known they would turn out so well.

— CNN’s Christina Zdanowicz contributed to this report.