A record-setting heat wave is blanketing much of the United States as millions of Americans gather for Independence Day, prompting the cancellation of events marking America’s 250th birthday.

Limited time: Save 25% on NBC News subscription

Get exclusive reporting, live Q&As and ad-free reading.

More than 87 million people are under extreme heat risk, according to the National Weather Service, while more than 150 million remain under heat alerts stretching from Kansas to Maine.

Several East Coast cities could break daily or all-time July temperature records Friday. Forecasters say Philadelphia could reach 103 degrees, just shy of its all-time July record of 104, while New York City’s Central Park is forecast to hit 102 degrees after reaching 100 degrees Thursday, its first triple-digital reading since 2012.

The dangerous temperatures have already disrupted several events scheduled for Friday. Philadelphia canceled its Wawa Welcome America parade, Washington’s Great American State Fair temporarily closed Friday afternoon, and other celebrations have delayed public entry to reduce exposure during the hottest hours.

Follow along for live updates.

The heat is also affecting rail travel. New Jersey Transit warned Friday morning that rail service is subject to delays of up to 30 minutes and select train cancellations due to the effects of extreme heat on equipment. Amtrak also warned that trains operating along the Northeast Corridor may run at reduced speeds between 11 a.m. and 7 p.m. through Saturday because of the heat.

Forecasters are also tracking severe thunderstorms across parts of the Midwest, Northeast and mid-Atlantic that could bring damaging winds, isolated tornadoes and flash flooding, potentially affecting holiday travel and evening fireworks displays.

Conditions are expected to begin improving across parts of the Northeast over the weekend, though the mid-Atlantic is forecast to remain dangerously hot.