Dangerous heat wave grips eastern U.S. through July 4 weekend

A prolonged, dangerous heat wave pushed heat indices to 111 degrees in Washington and 110 degrees in Philadelphia on Thursday, while New York City opened hundreds of cooling centers and Amtrak canceled more than two dozen trains in the Northeast. The National Weather Service forecast the worst of the heat to stretch through the Independence Day weekend across the eastern U.S., with peak heat indices possibly reaching 115 degrees in some areas.

In the Baltimore/Washington forecast area, record temperatures will continue through much of the holiday weekend, with widespread highs around 98 to 102 degrees and heat indices near 110. Relief may arrive early next week, but extreme heat and humidity will hold over the holiday, with the Mid-Atlantic and Southeast staying hot even as parts of the Great Lakes and Northeast cool slightly.

Philadelphia canceled the Salute to Independence Semiquincentennial Parade because of extreme heat. New York City activated its heat emergency plan, and Central Park hit 100 degrees, its first triple-digit day since 2012. New York City Public Schools and other city buildings will serve as cooling centers from 11 a.m. to 11 p.m. July 3 through July 5, a measure aimed at giving residents without reliable air conditioning a place to escape the heat.

New York City officials urged residents to conserve electricity as demand rose and load challenges grew, while the U.S. Department of Energy issued emergency orders to bring additional power plants online in the Mid-Atlantic ahead of peak demand. Tens of millions of people were under heat warnings expected to last into the July 4 holiday weekend, when Americans will mark the nation’s 250th anniversary.

Thunderstorms could complicate travel and outdoor gatherings, and the National Weather Service flagged an increased risk of severe storms through the weekend.