Millions of Americans are under heat advisories as high temperatures roast the U.S.

Heat Dome-Explainer
Hunter Van Dyne pauses to wipe sweat from his forehead inside a hot fireworks tent as he works to set up for the opening of Powder Monkey Fireworks, in Weldon Spring, Mo., on Monday.
Jeff Roberson/AP

A multi-day heat wave is still beating down on millions of people from the Midwest to the Northeast, with officials in multiple states declaring heat emergencies and urging people to take precautions as temperatures remain high.

As of Wednesday afternoon, the National Weather Service had issued heat advisories for parts of at least 15 states, including in several major cities such as Philadelphia, Columbus and Boston.

“Afternoon high temperatures and warm overnight lows will likely challenge daily records and even some monthly records,” the NWS said. “Those without access to reliable air conditioning are urged to find a way to cool down.”

Climate change increases the intensity and frequency of extreme heat.

Connecticut Gov. Ned Lamont initiated the state’s hot weather protocol. In New York, the maximum heat index — which combines temperature with relative humidity — was predicted to hover around 100 in some places on Wednesday. Gov. Kathy Hochul activated that state’s emergency operations center.

Boston Mayor Michelle Wu declared a three-day heat emergency in the city, which was also expecting a heat index in the high 90s or as high as 100. “Heat waves are a risk to our community, so everyone should make sure to stay hydrated, limit outdoor activity when possible, wear plenty of sunscreen, and check on your neighbors and loved ones,” Wu said.

Public schools in Buffalo and Rochester announced early dismissals this week due to the excessive heat, while Worcester Public Schools in Massachusetts decided to cancel classes on Thursday and end the school year early because of the sweltering weather.

Cooling centers were opened in multiple states. The National Weather Service said temperatures were expected to remain warm overnight as well, meaning those without air conditioning may not be able to cool down as easily and could face an even greater risk from the heat.

Pennsylvania officials have been issuing safety reminders to residents during what the commonwealth’s Sen. John Fetterman called “[o]ne of the most intense heat waves PA has seen in decades.”

CBS reported that more than 15,000 customers in the Pittsburgh area, which is under an excessive heat warning until 8 p.m. Saturday, had no power and may not get it restored until the weekend.

The NWS saidthe first major heat wave of the season should peak in the eastern Great Lakes and New England on Thursday, and last until Friday and into the weekend for the Ohio Valley and Mid-Atlantic.

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