'Brutal and dangerous' heat dome to grip New York City; Boston declares Heat Emergency

Potentially deadly heat dome tightens grip on eastern US this week

Tens of millions of people from the Plains to northern New England are under some kind of heat alert as a massive and potentially deadly heat dome advances off to the east, with many cities like Washington, Philadelphia and New York City possibly hitting 100 degrees. FOX Weather Meteorologist nick Kosir breaks down the forecast on June 22, 2025.

NEW YORK – An expansive heat dome that has already broken dozens of record-high temperatures on Friday and Saturday will continue Sunday, with more than 30 states on alert for potentially life-threatening heat through the first full week of summer.

The sprawling area of high pressure began to scorch the Plains and Midwest at the end of last week, breaking numerous records from Colorado, South Dakota and Nebraska through Minnesota, Wisconsin and Illinois.

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Denver tied its record high of 99 degrees on Friday, while Pueblo, Colorado, reached 103 degrees.

On Saturday, Minneapolis broke its old record that stood for more than 100 years when the temperature hit 96 degrees. St. Paul, Minnesota, tied its old record of 95 degrees. And in Mitchell, South Dakota, temperatures soared to 104 degrees, breaking its old record of 101 degrees set in 1988.

Heat alerts remain in effect across the Plains and Midwest through Sunday, with cities like Minneapolis, Chicago and St. Louis in an Extreme Heat Warning.

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New York City opens cooling centers; Boston declares heat emergency

Officials in several communities across the Northeast and New England have urged people to take proper safety precautions as the intense heat begins to build.

New York City Mayor Eric Adams held a news conference on Saturday and warned that the incoming heat wave would be "brutal and dangerous."

"Extreme heat will not just be uncomfortable and oppressive for New Yorkers," he said. "It’s going to be brutal and dangerous."

Adams said that every year, more than 500 New Yorkers die because of hot weather.

"It is imperative that we prepare ourselves," he said.

Connecticut Gov. Ned Lamont echoed those warnings and announced that he has directed the state’s Extreme Hot Weather Protocol to be activated and in effect from noon on Sunday through at least 8 p.m. on Wednesday.

"It looks like we are about to experience our first heat wave of the season, and when temperatures get this hot, people who are most vulnerable, especially those who are of a certain age or who have certain medical conditions, should take the necessary precautions to stay cool," Lamont said in a news release. "We are working with our partners to get cooling centers open across Connecticut."

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Boston Mayor Michelle Wu declared a Heat Emergency for the city through Tuesday due to the heat.

"With this Heat Emergency coming as we kick off the summer season, we ask our community members to please take care and prepare accordingly for the extreme heat," Wu said in a statement. "City staff are working to ensure that all residents can have a safe and enjoyable summer. Be sure to stay hydrated, take breaks from working outside and regularly check in on neighbors, friends, and family."

Splash pads have been opened at various parks throughout the city, and city pools have been made available for swimming.

The Boston Public Library will also be available for residents to seek relief from the heat.

Potentially deadly heat spreads into the Northeast this week

The heat dome will continue to spread east and will cast a wide net over more than half of the U.S., causing potentially life-threatening temperatures.

On Sunday, more than 190 million people will see temperatures at or above 90 degrees, with various heat alerts in effect from the Plains to northern New England.

High humidity with dew points into the 70s, if not near 80 degrees, will make temperatures feel like well over 100 degrees in cities like Chicago, Cleveland, Louisville in Kentucky, Nashville in Tennessee and Raleigh in North Carolina, according to the FOX Forecast Center.

The high humidity will also make for some uncomfortable evenings, with little relief from the extreme daytime high temperatures.

Heat alerts are in effect across the Northeast and New England through at least Wednesday as temperatures soar to levels not always seen during the month of June.

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Extreme Heat Warnings – the most dire heat alert issued by the National Weather Service – now stretch from Philadelphia up the Interstate 95 corridor into New York City, New Haven in Connecticut, Providence in Rhode Island and Boston.

Pittsburgh, as well as portions of West Virginia and New York state from the Hudson Valley to the U.S.-Canada border, are also under Extreme Heat Warnings.

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This graphic shows record-high temperatures in jeopardy of being broken on Monday and Tuesday.

(FOX Weather)

Triple-digit temperatures are forecast in New York City, Washington, Philadelphia and Hartford, Connecticut, on Tuesday.

New York City and Philadelphia have not hit 100 in any month since 2012. In New York City, the temperature had only reached 100 degrees in June three times prior, most recently on June 27, 1966. In Philadelphia, it has occurred 10 times before, most recently on June 15, 1994.

From the Gulf Coast to Massachusetts, heat indices will also top 100 degrees, making it dangerous for those working or playing outside without proper hydration or cooling options. 

Across the country, dozens of centuries-old heat records are threatened and likely to be broken by the end of this week. 

The heat should abate some starting Wednesday, but it'll still remain hot through the week as upper-level ridging remains in place.