Nearly 40 US cities, including Philadelphia, Baltimore, and Raleigh, North Carolina, broke daily heat records on Monday, with temperatures reaching up to 104 degrees (40C).
Over 150 million people were placed under heat warnings due to a "heat dome" phenomenon, with very warm overnight lows expected to continue through Wednesday.
The heat caused disruptions, including Amtrak delays due to speed restrictions on East Coast routes and the rescue of two 16-year-old hikers in New Hampshire who were overcome by the heat.