Record-Breaking September Heat Dome Sweeps South-Central U.S.

• A severe heat dome caused unseasonable, record-breaking temperatures across the south-central U.S. on September 15, 2026.
• Over 41 million people (approximately 12% of the U.S. population) were placed under extreme heat advisories, watches, or warnings.
• Several cities, including Dallas, Memphis, and Nashville, set new daily high-temperature records.

The Mechanism of a Heat Dome

• High pressure in the upper atmosphere traps hot air near the surface.
• This process suppresses convection, clouds, and precipitation, allowing intense solar radiation to further escalate temperatures.
• High humidity and calm winds contributed to dangerous heat index levels, increasing health risks for residents.

Contextual Climate Trends

• The mid-September event followed the warmest June-through-August period on record in the contiguous U.S. in 132 years.
• Summer 2026 was 0.4ºF (0.22ºC) hotter than previous record-setting summers in 1936 and 2021.