Forty million Americans faced extreme heat warnings Sunday across a sprawling corridor from California to Mississippi, as a second consecutive heat dome pushed heat indexes above 100 degrees Fahrenheit across central and southern states.
The National Weather Service projected temperatures reaching 120 degrees Fahrenheit in parts of the southwest, with humidity levels compounding the danger. The affected region stretched from Minnesota south to Mississippi and west into southern California and Nevada, covering some of the nation's most densely populated areas.
Extreme heat warnings signal conditions posing serious health risks within hours of exposure. The National Weather Service issues these alerts when heat indexes reach dangerous thresholds, typically above 103 to 105 degrees depending on regional acclimatization. Heat-related illness and death spike during such events, particularly among older adults, outdoor workers, and people without air conditioning access.
The persistence of consecutive heat domes reflects patterns consistent with climate change. As greenhouse gas concentrations rise, the atmosphere retains more heat, creating conditions where high-pressure systems linger longer over regions. Studies from the National Center for Atmospheric Research and similar institutions have documented an increase in the frequency, intensity, and duration of extreme heat events across North America over the past two decades.
This particular event stretched across multiple time zones and climate zones simultaneously, from the arid southwest to the humid southeast. The combination of heat and humidity in southern regions increases the danger substantially, as the human body struggles to cool through perspiration when the air already holds high moisture content.
Power grids face strain during extended heat events as cooling demand peaks. Utilities across affected states typically issue conservation notices requesting residents reduce electricity use during peak afternoon and evening hours to prevent blackouts. Water supplies also face pressure as agricultural irrigation and municipal demand surge.
The second consecutive day of warnings indicated the heat dome would persist rather than dissipate, a pattern that threatens public health infrastructure and increases wildfire risk across the southwest