Millions of Americans are facing oppressive heat, with forecasters expecting a "heat dome" to develop over parts of the county over the weekend and through next week. The National Weather Service (NWS) warns that heat related illnesses increase significantly during extreme heat events.

Shower chances hang around as the workweek nears an end, but extreme heat is on tap for Chicagoland this weekend.

The weather on Friday, the first day of summer, is pleasant in the Philadelphia region, with a high of 85 in the city and low humidity. But a heat wave could start Saturday with the mercury set to pass 90 degrees with high humidity making it feel even warmer.

The first major heat wave of the summer begins in the Plains and Midwest on Friday, and lasts through the weekend. The Northeast will see the heat and humidity peak early next week, with the heat wave lasting into Wednesday and Thursday for some.