The agency warned that extreme heat poses a danger in the evening as well, as temperatures are expected to remain above average overnight. As of Monday morning, nearly 8 million Americans were under heat alerts, according to the National Integrated Heat Health Information System.

What do you do when the sun won’t leave you alone day and night? More than 50 million people in the Western United States are under heat advisories this weekend, with temperatures soaring into the triple digits from Washington to Arizona.