At least 40 million people were under extreme heat warnings across central and southern parts of the United States on Sunday as high temperatures and severe humidity gripped large swaths of the country for a second straight day.
Heat indexes exceeding 105 degrees Fahrenheit stretched from Minnesota down to Mississippi, extending west into Southern California and Nevada. Parts of the Southwest could see highs of 120 degrees Fahrenheit on Sunday, according to the National Weather Service.
Meteorologists said the sweltering weather was the result of another heat dome — a phenomenon in which atmospheric conditions trap heat, accentuating and prolonging already high temperatures.
On Saturday, Rapid City, South Dakota, reported an all-time high of 112 degrees Fahrenheit. A horse race planned in Canterbury Park, in Shakopee, Minnesota, was canceled Sunday because of the heat.
“Right now, it’s affecting a lot of people right in the middle of the country,” said Bob Oravec, an NWS meteorologist. “The core of the heat sinks southward by early next week.”
The moist air was also producing other volatility around the top of the heat dome, including the risk of severe thunderstorms, flash flooding and hail around the Great Lakes on Sunday. The potential for heavy storms was expected to move east in the coming days.
“If you have a heat dome in one part of the country, you’ll have a different corresponding weather in another part,” Oravec said. “It’s all related.”
Temporary relief will come to the central U.S. toward the middle of the week, but high temperatures could return by the weekend, he noted.
Authorities warned that children and older adults, along with people with certain medical conditions, are especially at risk of serious reactions, including heatstroke. Experts recommend seeking out air conditioning or a cooling center, making sure to drink enough water and limiting time under the direct sun.
The continental U.S. endured the second-hottest first half of the year on record in 2026, according to tracking of average temperatures by the National Centers for Environmental Information.
