Heat dome pushes record temperatures across western U.S., prompting alerts for 55 million

An unusually strong heat dome is driving dangerously high temperatures across the western United States this weekend, affecting roughly 55 million people under heat alerts. The extreme heat stretches from southern California and Nevada through the Rocky Mountain states, with forecasts of up to 118°F in Phoenix and 115°F in Las Vegas.

The National Weather Service has issued "major" or "extreme" heat risk warnings for much of the region, indicating a heightened threat to public health. In Los Angeles, an extreme heat warning has led officials to open cooling centers through Sunday, while similar facilities are operating in Las Vegas and Phoenix.

"Extreme heat is the number one weather-related killer in the United States each year," the agency warned, noting that high nighttime temperatures in cities such as Phoenix and Las Vegas will limit relief for residents without access to cooling.

The Pacific Northwest faces an additional danger as a Level 3 "extremely critical" fire-danger rating has been applied to parts of Washington and Oregon. Washington Governor Bob Ferguson has imposed a statewide burn ban, and evacuation orders have been issued for Spokane County residents due to the Old Trails Fire. A Particularly Dangerous Situation Red Flag Warning was also issued for central and eastern Washington, reflecting the rare combination of strong winds, low humidity and ongoing drought.

Smoke from active wildfires is spreading across multiple states and into Canada, further compounding health concerns. Experts note that climate change is increasing the frequency and intensity of slow-moving heat domes like this one, though research on the trend continues.