Early heat dome brings record temperatures to eastern U.S.

An intense and nearly historic weather pattern is baking much of America under a dangerous heat dome this week, including places that haven't experienced such heat in more than a decade.

The heat wave is especially threatening because it's hitting cities like Boston, New York and Philadelphia early in the summer, when people haven't yet adapted to the broiling conditions, several meteorologists said.

The dome of high pressure parking over the eastern United States is trapping hot air from the Southwest that already made an uncomfortable stop in the Midwest.

A key measurement of the strength of the high pressure broke a record Monday and was the third-highest reading for any date, making for a "near historic" heat wave. The worst of the heat was likely to peak for Northeastern cities on Tuesday, forecasters said.

A heat dome occurs when a large area of high pressure in the upper atmosphere acts as a reservoir, trapping heat and humidity. A heat wave is the persistence of heat, usually three days or more, with unusually hot temperatures.

Nearly three-quarters of the country's population – 245 million people – will swelter with temperatures of 32 degrees Celsius or higher on Monday, and 33 million people, almost 10 percent of the country, will feel blistering 38 degrees Celsius on Tuesday. The government's heat health website showed the highest level of heat risk in swaths from Chicago to Pittsburgh and North Carolina to New York.

Those high air temperatures, with the feels-like index even worse because of humidity, are unusual for many places.

New York hasn't seen 38 degrees Celsius since 2011, and Philadelphia, which is forecast to have consecutive high temperatures, hasn't reached that mark since 2012.

In downtown Baltimore, temperatures climbed into the upper 30s Celsius by early Monday afternoon, bringing dozens of people to cool off at St. Vincent de Paul's resource center. A few blocks away, the city's historic Broadway Market food hall closed early when the building's air conditioning broke.

(Cover: Manhattan is shrouded in an afternoon haze seen from Staten Island in New York, the U.S., June 23, 2025. /VCG)