Heat records have fallen from Minneapolis to Macon, Ga.

For the third week in a row, it’s hot out there.

Much of the United States is in the midst of a third consecutive week of unrelenting heat, with sweltering temperatures stretching across the Southern Plains and the Mississippi Valley into the Great Lakes and the Deep South.

The week started off with 11 major cities breaking daily heat records, including Minneapolis reaching 101 degrees Fahrenheit on Monday. (The previous high for that date: 88 degrees, set in 1993.)

On Wednesday, 21 heat records were broken across the Ohio Valley and the Southeast. Nashville and Charlotte, N.C., both reached 101 degrees, breaking previous records of 100. And Macon, Ga., soared to 105 degrees, four degrees warmer than the record set in 1988.

As of Thursday morning, about 25 million people from Texas to southern Georgia remained under heat advisories issued by the National Weather Service.

Here’s a breakdown of the misery by region.

In the Midwest:

Daytime highs in the Great Lakes region soared into the mid-90s this week, almost 20 degrees above average for this time of year.

Chicago saw a high of 99 degrees this week, and it hit 96 degrees on Tuesday in Detroit, tying a daily record dating back to 1933. Rockford, Ill., about 80 miles west of Chicago, and Toledo, Ohio, both hit 100 degrees on Tuesday, tying records set in 1988, said Alex Lamers, a meteorologist with the Weather Service.

Heat concerns began to wane on Wednesday as a cold front pushed the heat to the southeast. Highs are forecast to drop into the 80s across the region on Thursday.

In the South:

The grueling temperatures across much of the United States this week are the result of what meteorologists call a heat dome — a high-pressure system that acts like a lid on a pot. Early in the week, it was centered on Georgia, Alabama, Tennessee, Kentucky and Ohio, said Brian Hurley, a meteorologist with the Weather Service.

Atlanta, where moist air usually keeps temperatures out of the extreme range (even if the humidity feels brutal), saw a high of 95 on Tuesday, three degrees shy of a record from 1933. The city also tied its heat record from 1964 on Wednesday, when it reached 98 degrees.

It was so oppressive that the Atlanta zoo closed early on Wednesday and planned to shorten operations again on Thursday, to avoid the hottest part of the day.

The heat dome shifted south on Wednesday, concentrating on the Mississippi Valley, the Gulf Coast states and northern Florida. By the end of the week, a stretch from Texas to the Florida Panhandle will carry the brunt of the heat, Mr. Lamers said, with temperatures reaching triple digits there.

Parts of the Gulf Coast had the greatest potential for record-breaking heat into the weekend, Mr. Lamers said. Some cities forecast to hit 100 or more include Tallahassee, Fla., and Baton Rouge, La.

On the coasts:

In Northern California, heat advisories were issued for much of Sacramento and the Bay Area on Wednesday. Highs did not climb above 100 degrees, but were in the high 90s farther away from the coastline.

States in the Northeast have largely been spared the heat. But a warm-up into the low 90s is forecast for some cities this weekend, including Philadelphia and Newark.

Looking ahead:

Temperatures across much of the country are expected to remain above normal for the next couple of weeks, according to the Weather Service. And beyond that, the National Oceanic and Atmospheric Administration has forecast a scorching summer for most of the United States.