Summer Goes Out With a Heat Dome
While astronomical summer was winding down, a heat dome brought sweltering conditions to the south-central United States in mid-September 2026. A NASA Earth Observatory map shows air temperatures across the contiguous U.S. on September 15, 2026, at 4 p.m. Central Time (21:00 Universal Time), modeled at 2 meters (6.5 feet) above ground. The map combines satellite observations with temperatures predicted by a version of NASA's GEOS (Goddard Earth Observing System) model, which uses mathematical equations to represent physical processes in the atmosphere; darkest reds mark areas approaching or exceeding 40°C (104°F).
On September 15, more than 41 million people in the U.S.—about 12 percent of the population—were under a National Weather Service extreme heat advisory, extreme heat watch, or extreme heat warning. The high temperatures spanned large parts of Texas, Oklahoma, Arkansas, Missouri, and Tennessee. Meteorologists warned that high humidity, limited cloud cover, and light winds could make temperatures feel higher than thermometer readings and increase the risk of heat-related illnesses.
Several locations set new daily high temperature records on September 15: Dallas, Texas, reached 101°F (38°C); Memphis, Tennessee, reached 99°F (37°C); and Nashville, Tennessee, reached 100°F (38°C). All three cities were at least 12°F warmer than normal that day, and Nashville broke its daily-high record from 1927. The day before, Nashville also set a record-high minimum temperature of 75°F (24°C). A weather phenomenon meteorologists call a heat dome was responsible: it develops when an area of high pressure in the upper atmosphere pushes hot air toward the surface and traps it there. Heat domes put the brakes on convection and suppress clouds and precipitation, allowing sunlight to reach Earth's surface relatively unhindered and further elevate air temperatures.
The stretch of unseasonable temperatures follows the warmest June through August in the contiguous United States in NOAA's 132-year record. The three-month period in 2026 was 0.4°F warmer than the previous records, set in 1936 and 2021. The image was produced by Michala Garrison using GEOS-FP data from the Global Modeling and Assimilation Office at NASA GSFC, with the story by Lindsey Doermann; sources include AccuWeather, Heat.gov, and NOAA National Centers for Environmental Information.