Meanwhile, millions of people are under heat advisories in the US cities of Boston, New York City, Philadelphia and as far west as Buffalo, New York, that will last through Wednesday.
The northern Plains, Midwest and Northeast will bear the brunt, with temperatures in Chicago forecast to reach 97F on Wednesday.
New York could reach 100F, while Washington DC is expecting 102F. A few places could get even hotter, with high humidity expected to make it feel even more uncomfortable.
Earlier this week, the city of Billings in Montana reached 111F, where its previous heat record was 108F. In Utah’s Salt Lake City, the previous record of 107F was broken when it reached 109F.
The high temperatures come not long after a record-breaking 4 July heatwave hit large portions of the US.
More than 165 million people sweltered under record temperatures along the US East Coast and Midwest, and at least 44 deaths were reported.
The heat also disrupted Fourth of July celebrations, including the Washington DC parade, which was cancelled.
Heatwaves have become more frequent, more intense and longer-lasting because of human-induced climate change. The world has already warmed by about 1.1C since the industrial era began and temperatures will keep rising unless governments around the world make steep cuts to emissions.