The thermometer at Salt Lake City International Airport reached 98 degrees at 2:45 p.m., according to the National Weather Service. That matched a record high set in 1947.
It was the second day in a row the city made new entries in the record books. The 100 degrees on Sunday beat the old record of 98 degrees set in 1995, the National Weather Service said.
That was also just the second time Salt Lake City reached triple digits in the month of September. The only other time was 100 degrees on Sept. 8, 1979.
The Wasatch Front as well as southern Wyoming and southern Idaho was under a red flag warning Monday with fire danger considered high.