Heat wave not seen in decades will send temperatures soaring for more than half the US population

(CNN) — A long-lasting and expansive heat wave fueled by an intense heat dome is underway for the Midwest and Northeast. Record-breaking high temperatures will last into next week, ushering in the start of summer with this year’s most significant heat event yet.

Hundreds of records could be tied or broken this week as a massive heat dome parks over part of the East. Multiple all-time June high temperature records could fall as the heat rises to levels normally seen only on the hottest July days. Parts of the Midwest to the Northeast could endure the longest heat wave they’ve seen in decades, the National Weather Service’s Weather Prediction Center said.

Not used to intense heat

Tens of millions of people who live as far north as Maine and aren’t used to heat this intense will be sweating in temperatures well into the 90s this week. It will feel even hotter than that as humidity helps drive heat index values – how temperatures feel to the body – into the low 100s.

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An extreme heat risk is in place from the Great Lakes into the Northeast this week, according to the National Weather Service. Wednesday and Thursday will be the hottest days of the week, but the surrounding days will only be slightly less brutal. Heat will reach dangerous levels in many places including the major metropolitan areas of Chicago, St. Louis, Detroit, Cleveland, Pittsburgh, New York City and Boston.

Temperatures will top out at 15 to 20 degrees above normal over a sweeping area of the northeastern US Monday afternoon and are expected to rise up to 25 degrees above normal through the rest of the workweek.

Some areas, including Montpelier, Vermont; Syracuse, New York; and Pittsburgh, haven’t seen heat like this in about three decades.

“Last time we saw heat in Pittsburgh like what we’re expecting next week was 30 yrs ago (almost to the day) when it reached 95°F or warmer for 6 straight days (June 15-20, 1994),” the local weather service office said on X. “That stands as the longest stretch of 95+ (degree) days on record. We have a shot at tying or beating that.”

Heat protocols

Some affected areas have started to activate heat protocols.

Cooling centers will open across New York City starting Tuesday and cooling kits will be distributed to people working outdoors, Mayor Eric Adams said Monday. Burlington, Vermont, will also activate cooling centers starting Tuesday, according to the city.

Recreation centers in Cleveland will be open for extended hours this week to serve as cooling centers, city officials said Monday. The city also suspended all playground programs for the week as temperatures soar.

Heat domes like the one fueling this week’s intense conditions trap air in place and bake it with abundant sunshine for days on end, making each day hotter than the last. The oven-like conditions mean overnight temperatures often don’t cool down enough to offer relief for overheated bodies, posing increased risks for heat-related illness.

“Warm overnight temperatures only dropping into the mid-70s will offer little to no relief, especially to those without adequate or reliable cooling,” the Weather Prediction Center said.

Humidty and extreme heat

Humidity will also join forces with extreme heat to create triple-digit heat indices – measurements of how hot the human body feels – in some areas.

Chicago residents could feel heat indices between 95 and 105 degrees through next week, the NWS in Chicago warned. Parts of eastern New York and western New England could see indices as high as 107 degrees.

The NWS in Detroit, where the heat index could reach 100 degrees, urged residents to practice heat safety in the coming days, including limiting strenuous outdoor activities, staying hydrated, and checking up on neighbors who are elderly or don’t have A/C.

Heat-related illness is a concern in severely impacted areas, particularly for the elderly, young children and outdoor workers. Extreme heat is by far the deadliest form of severe weather, killing on average twice as many people a year as tornadoes and hurricanes combined.

Scientists have warned that heat waves will become increasingly severe as the climate crisis intensifies.

CNN’s Robert Shackelford, Celina Tebor and Zenebou Sylla contributed to this report.