Summer will make a dramatic entrance in the U.S. this week with a heat dome that will bring stifling temperatures and uncomfortable humidity to millions.

The heat will be particularly worrisome this weekend across wide stretches of Nebraska, Illinois, Wisconsin and Iowa, where forecasters are warning of extreme temperature impacts.

This will be the first stretch of true summertime weather for many from Midwest to the East Coast, said Tom Kines, a meteorologist at the private weather company AccuWeather.

“A lot of those folks have been saying, where’s summer? Well, buckle up, because it’s coming,” said Kines. The humid conditions will make places that exceed 90 degrees Fahrenheit feel as much as 20 degrees hotter, Kines said.