Earth ObservatoryScienceEarth ObservatorySummer Goes Out With a Heat DomeEarthEarth ObservatoryImage of the DayEO ExplorerTopicsAll TopicsAtmosphereLandHeat & RadiationLife on EarthHuman DimensionsNatural EventsOceansRemote Sensing TechnologySnow & IceWaterMore ContentCollectionsGlobal MapsWorld of ChangeArticlesEarth Matters BlogBlue Marble: Next GenerationEO KidsMission: BiomesAboutAbout UsSubscribeđ RSSContact UsSearch An area of high pressure over the south-central U.S. produced unseasonable and, in some places, record-breaking warmth on September 15, 2026, as shown in this map of modeled air temperatures from GEOS (Goddard Earth Observing System).NASA Earth Observatory/Michala GarrisonWhile 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.DownloadsSeptember 15, 2026JPEG (1.22 MB)References & ResourcesAccuWeather (2026, September 11) Latest heat dome to linger in south-central, southeastern US in mid-September. Accessed September 16, 2026.Heat.gov (2026) Science and Information to Reduce Heat Risk. Accessed September 16, 2026.NOAA National Centers for Environmental Information (2026, September 9) Warmest summer on record for the contiguous U.S. Accessed September 16, 2026.The Washington Post (2026, September 15) Itâs almost fall, but this record heat dome didnât get the memo. Accessed September 16, 2026.You may also be interested in:Stay up-to-date with the latest content from NASA as we explore the universe and discover more about our home planet. Heat Dome Broils the Western U.S. 4 min read A ridge of high pressure fueled record-breaking temperatures in Montana, Utah, and Wyoming on July 12, 2026.Article Europeâs Scorching Summer 6 min read A series of heat waves in 2026 is breaking records and taking a toll in Europe.Article Sensing the Polesâ Hidden Heat 3 min read New animations from NASAâs PREFIRE mission reveal two years of seasonal temperature swings at the Arctic and Antarctic.Article1234NextKeep ExploringDiscover More from NASA Earth ScienceSubscribe to Earth Observatory NewslettersSubscribe to the Earth Observatory and get the Earth in your inbox.Earth Observatory Image of the DayNASA’s Earth Observatory brings you the Earth, every day, with in-depth stories and stunning imagery.Explore Earth ScienceEarth Science DataOpen access to NASAâs archive of Earth science data