Tens of millions of Americans are bracing for prolonged dangerous heat as a persistent heat dome anchored over the Western United States begins pushing eastward toward the Central Plains and Midwest.

Meteorologists at the National Weather Service have expanded excessive heat warnings and heat advisories across more than a dozen states. Daytime highs in parts of California, Nevada, and Arizona are soaring past 110 degrees Fahrenheit (43°C), with major metropolitan areas in the region offering extended cooling center access to offset severe health risks.

Weather models indicate the high-pressure system will move across the Rocky Mountains and into the central U.S. in the coming days, dragging triple-digit heat and intense humidity into areas unprepared for late-season extremes. Combined with high overnight lows that provide little relief, officials warn that heat-related illnesses like heat exhaustion and heatstroke could spike dramatically.

“This is not standard summer weather — it is a prolonged, high-risk thermal event,” forecasters stated in an update. Public health agencies urge residents across affected zones to stay indoors during peak afternoon hours, maintain proper hydration, and frequently check on vulnerable neighbors and elderly relatives.