‘Extraordinarily hot’: US heatwave stretches on with millions still under warnings

Southern and central states from California to Mississippi face heat indexes above 100F amid another heat dome

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 well above 100F (38C) stretched from Minnesota down to Mississippi , extending west into southern California and Nevada. Parts of the south-west were expected to see highs of 120F (49C), 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.

“It’s extraordinarily hot,” said Pete Miller, an outreach manager for the homeless services network Threshold CoC, which was passing out water bottles to residents in Omaha, Nebraska, on Sunday.

“We’re seeing a lot of people who are exhausted, drained by the heat in a way that is really dangerous ,” Miller added. “The humidity is insane. You stand outside for 30 seconds and you get drenched. And it’s going to be like that all night.”

Rapid City, South Dakota , reported an all-time high of 112F on Saturday. A horse race planned in Canterbury Park in Shakopee, Minnesota, was canceled on 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 US 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 conditions including heat stroke or even death. Experts recommend seeking out air conditioning or a cooling center, make sure to drink enough water and limit time under the direct sun.

Extreme heat events are increased and exacerbated by the climate crisis , which comes from the burning of fuels including gasoline, oil and coal.

The continental US endured the second-hottest first half of the year on record in 2026, according tracking of average temperatures by the National Centers for Environmental Information.