Summer Goes Out With a Heat Dome
While the calendar indicated that astronomical summer was winding down, a swath of the south-central United States was sweltering under a heat dome in mid-September 2026.
This map shows air temperatures in 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 the ground. It was produced by combining satellite observations with temperatures predicted by a version of the GEOS (Goddard Earth Observing System) model, which uses mathematical equations to represent physical processes in the atmosphere. The darkest reds indicate areas where temperatures approached or exceeded 40 degrees Celsius (104 degrees Fahrenheit).
More than 41 million people in the U.S.âabout 12 percent of the populationâwere under a National Weather Service extreme heat advisory, extreme heat watch, or extreme heat warning on September 15. The high temperatures spanned large portions of several states, such as 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. These included Dallas, Texas, at 101ÂșF (38ÂșC), Memphis, Tennessee, at 99ÂșF (37ÂșC), and Nashville, Tennessee, at 100ÂșF (38ÂșC). The cities were all at least 12ÂșF warmer than normal that day, with Nashville breaking its daily-high record from 1927. The day before, Nashville also set a record-high minimum temperature of 75ÂșF (24ÂșC).
A weather phenomenon meteorologists call a heat dome was responsible for driving temperatures up across the region. A heat dome 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. This allows sunlight to reach Earthâs 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 a 132-year record, according to NOAA. The three-month period in 2026 was 0.4ÂșF warmer than the previous records, set in 1936 and 2021.
NASA Earth Observatory image by Michala Garrison, using GEOS-FP data from the Global Modeling and Assimilation Office at NASA GSFC. Story by Lindsey Doermann.
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Full text from nasa.gov (public domain).