Extreme temperature warnings in place as 'heat dome' bakes US

More than 150 million Americans are under extreme heat warnings as a persistent heat dome continues to bake large swathes of the country, with temperatures in parts of the Southwest and Midwest reaching levels that the National Weather Service has described as "life-threatening."

The heat dome, a high-pressure system that traps hot air over a region, has been parked over the central United States for more than a week and is expected to persist for at least another five days. Phoenix, Arizona, has recorded 23 consecutive days above 43°C, while Chicago, less accustomed to extreme heat, has seen temperatures exceed 38°C for four days running — the longest such streak in the city's recorded history.

The health impacts are mounting. Hospitals across the affected states are reporting a surge in heat-related admissions, with emergency departments in Phoenix and Las Vegas operating at or above capacity. The death toll, while difficult to measure in real time, is expected to run into the hundreds. The 2025 heat season killed an estimated 2,300 Americans, and public health officials say 2026 is on track to be worse.

The heat is also testing critical infrastructure. Power grids in Texas and California have avoided blackouts so far but are operating with minimal reserve capacity. Amtrak has reduced speeds on several routes because of concerns about track buckling. And in parts of the Midwest, the heat has been accompanied by high humidity that dramatically reduces the body's ability to cool itself through sweating.

Climate scientists say the frequency and intensity of heat domes has increased measurably as a result of global heating, and that events currently described as exceptional will become typical within two decades if emissions continue on their current trajectory.