Nevada had its warmest August on record. Arizona tied its hottest summer, while New Mexico, Utah and Colorado logged their hottest summers ever, according to data from the National Oceanic and Atmospheric Administration.
The heat was especially pronounced across the Southwest, where daytime highs averaged 90.9 degrees this summer — 5.6 degrees above average and nearly 1 degree warmer than the previous record set in 2020.
Farther north, Wyoming shattered records in July. Temperatures there averaged 6.3 degrees above the 20th-century average, making it both the state's hottest July and hottest month ever recorded.
Idaho was the only state in the region that didn't break a statewide temperature record this summer.
The records were part of an exceptionally hot summer nationwide. The contiguous U.S. averaged 74.4 degrees from June through August, which is 3 degrees above the 20th-century average and the hottest summer in 132 years of recordkeeping.
Several factors fueled the record heat
No single cause drove the exceptional warmth, experts say.
Marc Alessi, a climate scientist with the nonprofit Union of Concerned Scientists, said a strengthening El Niño played a role, along with unusually warm ocean temperatures and the long-term warming of the planet caused by human activities, primarily, the burning of fossil fuels.
Those shorter-term factors are unfolding against a warmer baseline. As greenhouse gases accumulate in the atmosphere, they trap additional heat, increasing the likelihood and intensity of extreme temperatures.
For the West, Alessi said the consequences extend beyond hotter summer days.
“Even if the interior West gets a normal amount of precipitation, the issue is that the West will still be significantly drier because the atmosphere is warmer,” Alessi said. “It’s sucking up more moisture from the ground.”
That drying can also raise the risk of flash flooding when heavy rain arrives, as parched soils struggle to absorb the sudden rush of water.
Heat can make a dry West even drier
Warmer air can increase evaporation and pull more moisture from soils and vegetation. That means landscapes can dry out faster, worsening drought conditions, stressing water supplies and increasing wildfire risk.
Heat and drought can also reinforce each other. As soils become drier, Alessi said, less moisture is available to cool the land through evaporation.
Alessi said summers like this one offer a glimpse of how temperature extremes are changing as the climate warms.
“These events that should be uncommon, or almost never happen, are happening and becoming more frequent and intense,” he said.
This story was produced by the Mountain West News Bureau, a collaboration between Boise State Public Radio, Wyoming Public Media, Nevada Public Radio, KUNR in Nevada, KUNC in Northern Colorado, KANW in New Mexico, Colorado Public Radio and KJZZ in Arizona as well as NPR, with support from affiliate newsrooms across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting and Eric and Wendy Schmidt.
