A heat dome, characterized by extreme heat and humidity, is expected to cover most of the United States and affect more than 220 million people.

Temperatures are forecast to exceed 90 degrees, and for those living in the Northeast and Mid-Atlantic, temperatures are expected to exceed 100 degrees. Dangerous heat indexes are expected in most of the country.

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As of early Thursday, extreme heat watches, warnings, and advisories have been announced in the Southwest, Rockies, Plains, Upper Midwest, and parts of the Northeast U.S.

It will be the first scorching summertime weather of the year for most people in the Midwest and Northeast. 

“A lot of those folks have been saying, ‘Where’s summer?’ Well, buckle up, because it’s coming,” Tom Kines, a meteorologist at the private weather company AccuWeather, told the Associated Press.

The National Weather Service Weather Prediction Center predicts the heat wave will hit next week. Daytime temperatures will be in the 90s, and overnight temperatures will only drop to the mid-70s from the Great Lakes to the East Coast. It will be muggy as moisture blows north from the Gulf.

Most of the U.S. will see extreme heat by the end of the week. On Friday, Denver could reach 100 degrees, Chicago could reach 96 degrees by Sunday, and Washington, D.C., could see a high of 99 degrees on Tuesday. 

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It will likely feel hotter than these temperatures because the heat index, which measures how it feels outside to account for humidity, is expected to be in the triple digits. Accounting for humidity, it could feel as hot as 110 degrees, most notably in the Mid-Atlantic region.

Heat is the deadliest form of extreme weather in the U.S., killing more than 800 people per year on average since 1999, according to a 2023 study.