A heat dome brought record-breaking temperatures to the south-central United States in mid-September 2026, impacting millions and following the warmest summer on record. NASA modeled air temperatures on September 15, 2026, revealing areas exceeding 40 degrees Celsius (104 degrees Fahrenheit).
More than 41 million people – approximately 12 percent of the U.S. population – were under National Weather Service extreme heat advisories, watches, or warnings on September 15. The high temperatures affected large portions of Texas, Oklahoma, Arkansas, Missouri, and Tennessee. Meteorologists cautioned that high humidity, limited cloud cover, and light winds could exacerbate the heat, increasing the risk of heat-related illnesses.
Several cities recorded new daily high temperature records on September 15, including Dallas, Texas, at 101ºF (38ºC); Memphis, Tennessee, at 99ºF (37ºC); and Nashville, Tennessee, at 100ºF (38ºC). Nashville was at least 12ºF warmer than normal, breaking its daily high record from 1927. The day prior, Nashville also set a record-high minimum temperature of 75ºF (24ºC).
The phenomenon responsible for the extreme heat is a heat dome, which forms when high pressure in the upper atmosphere traps hot air near the surface. This suppresses convection, cloud formation, and precipitation, allowing more sunlight to reach the Earth and raise temperatures. According to NOAA, June through August 2026 was the warmest such period in a 132-year record, exceeding previous records set in 1936 and 2021 by 0.4ºF.
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