A brutal late July heat wave has 62 million people under heat alerts stretching from northern Florida to the northern Plains.

A heat dome is expected to strengthen over the Mississippi and Ohio valleys, bringing triple-digit temperatures from Kansas to Mississippi. The heat will expand over the Upper Midwest midweek, then cross into the East Coast on Friday.

Some major cities under heat alerts include New Orleans; Memphis, Tennessee; Little Rock, Arkansas; St. Louis; Kansas City, Missouri; Chicago and Minneapolis. Meanwhile, Mobile, Alabama, and Pensacola, Florida, are expected to set record highs.

Temperatures will sizzle in the upper 90s, high enough to set localized daily records in the Southeast. Heat indexes from the central Plains to the Southeast will range between 100 and 110 degrees Fahrenheit each day, with localized readings potentially reaching 115, the National Weather Service said.

“There is high confidence that heat will reach levels that would affect anyone without sufficient cooling and/or adequate hydration, particularly Tuesday through Thursday over the Mid-Mississippi Valley and Mid-South Regions,” it warned.

In the Northeast, temperatures and humidity levels are expected to increase Wednesday, with heat peaking Friday, when record warmth and heat index values of 95 to 100 are forecast to reach the region.

Nearly half the U.S. population is at least three times more likely to experience extreme heat due to human-caused climate change, according to a Climate Central analysis.

Officials warn locals to stay hydrated, take breaks from being outdoors, apply sunscreen every two hours, and wear lightweight, loose-fitting and light-colored clothing during heat waves.

While scorching temperatures are a significant concern this week, thunderstorms will drench other parts of the country.

On Tuesday, thunderstorms will pose a flash flood threat in parts of the Southwest, the Midwest and the Southeast, with a slight risk, a threat level of 2 out of 4, for flash flooding in portions of the Upper Midwest and the Southwest, according to the weather service.

Flood watches are in effect for northern Minnesota and northern Wisconsin, as well as much of New Mexico, due to the potential for heavy rain through Tuesday night.

Cities to watch include Duluth, Minnesota, and Albuquerque and Ruidoso, New Mexico, which were hit with historic and deadly flooding earlier this month.

Up to 1 to 3 inches of rain are expected to fall across the Upper Midwest, with locally higher amounts possible. For the Southwest, monsoon storms could produce rainfall rates of 1 to 2 inches per hour, which could spark sudden flash flooding if they fall over burn scar areas.

There is a slight risk for severe storms for 5 million people from the northern Rockies to the Upper Midwest on Tuesday. By Wednesday, 6 million people are at risk again, from the northern Plains to the Upper Midwest.