Heat dome brings record-breaking temperatures to western U.S. states

Severe weather alerts covered roughly 40 million people across the western United States as a heat dome reached its peak Sunday, July 12, 2026, putting emergency rooms, power systems and outdoor workers under the same relentless pressure. The hardest hit areas were the northern Plains, the Rockies and sections of the desert Southwest, where forecasters warned of widespread highs between 105 and 115 degrees.

The National Weather Service warned the danger was not limited to the afternoon spike. Record-warm lows were expected to offer little overnight relief, extending heat stress over several days. Hazardous heat would spread eastward at times while lingering through next weekend.

In Montana, the weather service office in Billings warned temperatures could reach all-time highs Sunday, with readings potentially climbing to 112 degrees. Most of Utah was under an extreme heat warning set to remain in place through Tuesday morning, while forecasters in Bismarck, North Dakota, forecast heat indices from 100 to 110 degrees through Monday. In western Colorado, afternoon temperatures were forecast to reach 98 to 102 degrees in some areas, and the Four Corners and Paradox Valley region was expected to see 97 to 102 degrees.

The heat could strain health systems, industries and infrastructure, while also raising wildfire risk and the danger of heat-related illnesses, including heat stroke. National Weather Service advisories urged people to drink plenty of fluids, stay in air-conditioned rooms, stay out of the sun and check on relatives and neighbors. Heat alerts are issued when an extreme heat event is occurring, imminent or highly likely, and heat is the deadliest weather hazard in Arizona.