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.

Weather forecasters have warned of extreme and dangerous temperatures as a major heat wave sweeps across the central and eastern U.S. states.

A Midwest heat dome will bring worryingly high temperatures and stifling humidity to millions of people 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.