First Day of Summer Will Bring Massive Heat Wave

Friday will be the first day of summer—and the first day of a massive heat wave in parts of the country that experienced an unusually mild spring. With a "heat dome" moving east, temperatures are expected to top 90 degrees for around 220 million Americans in the days to come, with temperatures of 100 degrees or more for 35 million, including some in Northeast and Mid-Atlantic states, the Washington Post reports. Forecasters say the heat—likely to break records in some places—and extreme humidity will last for around a week.

AccuWeather meteorologist Tom Kines says this will be the year's first stretch of hot weather for many people from the Midwest to the East Coast, the AP reports. "A lot of those folks have been saying, 'Where's summer?' Well, buckle up, because it's coming," he says.

Forecasters say heat that has been trapped over the West will move east on Thursday, with the Central Plains and Upper Midwest heating up on Friday and extreme heat reaching the East Coast on Saturday, the New York Times reports. Many cities in the heat wave's path haven't experienced a single 90-degree day so far this year, and Alex Lamers at the Weather Prediction Center warns that the heat could be especially dangerous because people are not acclimatized to it. (More heat wave stories.)