Heat Dome Broils the Western U.S.

It’s still relatively early in the summer season in the Northern Hemisphere, but several parts of North America were sweltering in mid-July.

The latest purveyor of heat was a strong ridge of high pressure that lingered in the upper atmosphere over the northern Rockies on the weekend of July 11-12, 2026. This pushed hot air toward the surface and trapped it there—a weather phenomenon meteorologists call a heat dome.

Heat domes put the brakes on convection and suppress clouds and precipitation. This allows sunlight to reach Earth’s surface relatively unhindered and further elevate air temperatures. As a result of the July heat dome, sites in Montana, Wyoming, and Utah broke all-time temperature records.

The map above shows air temperatures across the United States on July 12, 2026, at 2 p.m. Mountain 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 45 degrees Celsius (113 degrees Fahrenheit).

A preliminary analysis from the National Weather Service office in Billings found that temperature sensors at airports in Billings and Miles City, Montana (111°F and 115°F, respectively), and Sheridan, Wyoming (109°F), all recorded new all-time record highs on July 12. Each of these stations topped its previous record by at least 2°F, with Miles City breaking its record by a full 4°F. The Montana records date to the 1930s; the Sheridan record begins in 1907.

Multiple locations in Utah broke all-time records as well, according to the National Weather Service office in Salt Lake City, including Deseret (111°F), Salt Lake City (109°F, or 4°F above the previous record), and Randolph (100°F, or 6°F above the previous record). These stations in Utah have records that date back to the 1890s.

Extreme heat doesn’t just make people uncomfortable. It can have serious health consequences, particularly for older people. Extreme heat worsens common age-related health conditions such as heart, lung, and kidney disease. Health tracking data from the U.S. Centers for Disease Control and Prevention shows that the rate of heat-related emergency department visits in the Mountain states spiked tenfold during the July heat.

Heat waves like this one have become more frequent in the United States in recent decades, according to researchers at NASA’s Goddard Space Flight Center. Using a NASA modeling system called MERRA-2 (Modern-Era Retrospective analysis for Research and Applications-2), one NASA team found that summer heat waves in the U.S. roughly doubled in number between 1980 and 2023, increasing from an average of two to four per month.

Forecasters expect the heat dome to spread east into the Midwest, New England, and the Mid-Atlantic in the coming days, where triple-digit temperatures are likely in some areas. The United States isn't alone in facing significant heat. Parts of both Western Europe, Central Asia, and East Asia are also facing heat waves.

NASA Earth Observatory image by Michala Garrison, using GEOS-FP data from the Global Modeling and Assimilation Office at NASA GSFC. Story by Adam Voiland.

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Full text from nasa.gov (public domain).