Heat Dome Threatens Record Highs From D.C. to New York by July 4

Washington and Baltimore are forecast to come within a few degrees of their all-time record highs of 106 and 107 degrees Fahrenheit this week, and they are not the outliers. A heat dome — a ridge of high pressure that traps hot air in place — has settled over the eastern two-thirds of the country, and the National Weather Service says more than 165 million people are now at major or extreme risk from heat-related illness.

The numbers are specific enough to plan around. Heat indices, which combine temperature and humidity into a single “feels like” figure, are forecast to hit 104 degrees in Chicago, 109 in Detroit, 104 in New York City, 107 in Philadelphia, 108 in Washington and 111 in Nashville over the coming days, according to forecasts. Philadelphia’s health department declared a heat emergency running from Wednesday morning through 8 p.m. Saturday — a window chosen because overnight lows in the mid-70s to low 80s won’t let bodies recover before the next day’s heat resumes.

The World Cup is inside the heat dome, too

The timing collides directly with the tournament’s knockout rounds. An extreme heat warning covers Philadelphia through the evening of the Fourth, when the city hosts Paraguay against France at 5 p.m. with temperatures forecast near 100 degrees and little relief after dark. We are definitely getting into the hottest part, said Daniel Vecellio, a climate scientist at the University of Nebraska at Omaha who studies extreme heat. This is definitely the week, and coming up this weekend, where some of these systems will be tested.

FIFA has added an extra water break per half and installed air conditioning on team benches for matches played in the worst of it, and fans are permitted to bring one factory-sealed water bottle into stadiums. The governing body did not respond to questions about whether it had added shade, misting stations or free water for people waiting in line outside — the parts of the heat plan that affect fans rather than players.

Vecellio’s warning extends beyond game days. There are lots of different ways to be vulnerable to the heat. One of the biggest ones is age, he said, noting that older adults sweat less and regulate body temperature less efficiently, while people with heart disease face added cardiovascular strain in hot, humid conditions.

This is the first widespread heat wave of the summer, covering more than half the country at once, and it follows the same pattern that pushed Germany to a national heat record just days ago. High heat is forecast to persist across the Great Plains, Southeast and mid-Atlantic into next weekend, even as an unusual pocket of the Pacific Northwest stays 20 to 35 degrees below its seasonal average — a reminder that a heat dome redistributes the atmosphere’s heat as much as it adds to it.