As temperatures in Phoenix finally drop closer to normal — or even below average — for this time of year, the desert heat has likely cooled until next spring. But this year was one for the record books.

America’s hottest city broke record after record this summer — the hottest summer on record — and well into autumn, some set only a year ago and others just the day before. 

Meteorologists attribute Arizona’s hot summer to weather patterns, a dry monsoon, climate change and Phoenix’s urban heat island — a phenomenon where roads, buildings and infrastructure absorb and re-emit the sun’s heat, making cities hotter. 

“This year, while we may not have had quite extremes in terms of daily high temperatures, we’ve seen the temperatures persist,” said Sean Benedict, the lead meteorologist at the National Weather Service in Phoenix. “This year we had a record-hot June, so it started early and it persisted.” 

A high–pressure system, sometimes referred to as a heat dome, settled over the Southwest for most of the summer and into the fall, trapping hot air below and reducing cloud cover. The monsoon was also sporadic, providing little rainfall to alleviate temperatures. 

Phoenix wasn’t alone in breaking records. Arizona cities like Flagstaff, Yuma, Kingman and Winslow had their hottest summers on record and Tucson and Douglas tied with previous records.

Above-normal temperatures have been observed across the U.S. from summer through the fall, with the Southwest observing temperatures from 10 to 20 degrees higher than normal in some cases. 

Climatologists are concerned by the frequency of new records and believe the trend is further evidence of the role climate change plays in above-average temperatures and extreme weather. 

“The things that were rare are becoming less rare,” said Michael Crimmins, climatologist for the University of Arizona. “Everybody knows it’s hot here in the summer, and you think ‘Well, it can’t be that hot again next summer,’ and then it is.”

Hayleigh Evans writes about extreme weather and related topics for The Arizona Republic and azcentral.com. Email her with story tips at hayleigh.evans@arizonarepublic.com.