The heat dome arrives just before the Fourth of July weekend, when AAA predicted 72.2 million Americans would travel.

Heat domes trap overnight temperatures too — and millions without air conditioning are facing this week's Eastern U.S. heat wave.

A prolonged, dangerous heat wave will continue to intensify across most of the central to eastern U.S. into the Fourth of July weekend.

Heat-trapping high pressure systems can sit over an area for a week or longer

In the U.S., hundreds of people succumb to heat-related illnesses each year

High humidity is expected to make conditions feel even hotter