Scores of millions of people across the central and eastern US will swelter under the summer’s first “heat dome” beginning this weekend and extending through the end of next week as extreme hot air and humidity get trapped in the atmosphere.
The arrival of the heatwave coincides with Friday’s first day of summer and will bring temperatures at or above 100F (37.7C) to numerous cities as it moves to the east of the US in the coming days, forecasters say.
As estimated 170 to 200 million people will be affected from the central Great Plains to mid-Atlantic states including New York, New Jersey, Massachusetts and Pennsylvania, with no respite expected until the “lid” of strong high pressure eases by next weekend.
Experts are warning residents to stay cool indoors as much as possible, even after darkness falls.
“It will be exceptionally warm at night with little relief once the sun goes down,” Bernie Rayno, chief on-air meteorologist at AccuWeather, said in a Friday afternoon bulletin. “Many urban areas may struggle to drop below 80 at night, and that can take a toll on the body without air conditioning.”
Heat domes, which form when high pressure from Earth’s atmosphere compresses warm air and pushes it down to the surface, have become increasingly common in the US in recent years amid rising global temperatures fueled by the climate emergency.
Extreme heat has killed more people in the US since 1995 than hurricanes and tornadoes, National Weather Service figures show, including 238 last year.
“Extreme heat is tragically the leading cause of weather-related fatalities in America,” Jonathan Porter, AccuWeather’s chief meteorologist, said.
“There is an amplified risk of heat-related illnesses because this is the first heat wave of the year for millions of people, and their bodies are not yet acclimated to this type of heat and humidity.”
More than 40 million people were already under heat alerts by Friday lunchtime as temperatures began to rise across the midwest. Large areas of Kansas, Nebraska and Iowa were experiencing temperatures above 90F.
On Saturday, extreme heat is forecast to spread north and east into Minnesota, Wisconsin, Illinois and Missouri; while Sunday will see states including Ohio, Pennsylvania and New York beginning to experience peak temperatures.
By early to midweek, the entire region stretching as far east as Maine will have high temperatures and humidity.
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The health risks of the extreme heat cannot be underestimated, experts say, especially if temperatures do not drop significantly after the sun sets.
“Your body needs a reprieve,” Ashley Ward, director of the Heat Policy Innovation Hub at Duke University, told the Associated Press.
“You don’t get that overnight, we start the next day at a deficit. When we have overnight temperatures that don’t drop below 75F you start to see some pretty extraordinary outcomes with respect to heat illness and heat stroke, and even mortality.”
Some states and municipalities have set up cooling stations to ease conditions for vulnerable populations, especially those who are unhoused.
Only a handful of states have legal heat protections such as shade and water breaks for outdoor workers. In Phoenix, Arizona, the hottest city in the US with 143 days at or above 100F in 2024, city leaders last year unanimously approved regulations including mandatory access to air conditioning.
Some states, however, have actively removed such measures. In Florida, which has an estimated 2 million outdoor workers, Republican governor Ron DeSantis signed a law last year banning municipalities from enacting heat protections after lobbying from business owners.
