Heat dome to push triple-digit temperatures across Western US through weekend

What is a heat dome?

In the Southwest, cities including Las Vegas and Phoenix are expected to remain at the core of the heat through the weekend, with daytime highs climbing well above 110 degrees Fahrenheit and overnight lows offering little relief. Local officials have urged residents to limit outdoor activity during peak afternoon hours, check on elderly neighbors, and use cooling centers where available.

Northern-tier states face a different but related concern: the rapid onset of conditions far above average for August. Meteorologists tracking the system, including those cited by AP-affiliated outlets, have noted that the magnitude of the anomaly — the gap between forecast highs and historical norms — may be more consequential in places like Montana than the absolute temperature reading, because communities there are less adapted to sustained extreme heat.

Utility operators across the region have warned that electricity demand is likely to spike as residents run air conditioning at full capacity. Grid managers in California and the desert Southwest have issued calls for voluntary conservation during evening peak hours to reduce the risk of rolling outages, though no formal emergency has been declared.

Health and grid warnings

Public-health agencies have reiterated guidance on heat illness, noting that heat exhaustion and heat stroke can develop quickly when temperatures climb above 100 degrees, particularly among older adults, young children, outdoor workers, and people without reliable access to air conditioning. Officials are urging residents to drink water before feeling thirsty, wear lightweight clothing, and never leave children or pets in parked vehicles.

Air quality is also expected to deteriorate in some areas as the heat bakes pollutants into a shallow layer near the surface. The combination of high ozone readings and extreme heat can worsen respiratory conditions, particularly for people with asthma or other chronic lung diseases.

Outlook for next week

Forecasters expect the ridge to gradually weaken early next week as it shifts east, but they caution that residual warmth and elevated overnight temperatures could persist for several days afterward. Long-range outlooks suggest above-average temperatures may continue across much of the Western United States through the middle of August, raising the prospect of compounding heat events in regions already parched by a dry summer.

Across the affected states, schools, employers, and event organizers have begun adjusting schedules. Outdoor athletic practices have been moved to early morning hours, and some municipalities have extended the hours of public pools and libraries serving as cooling sites.