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

The latest provider of heat was a strong high-pressure ridge that remained 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.

Thermal domes slow convection and suppress clouds and precipitation. This allows sunlight to reach the Earth’s surface relatively unhindered and further raises 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 in 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 Goddard Earth Observing System (GEOS) model, which uses mathematical equations to represent physical processes in the atmosphere. Darker 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 the airports in Billings and Miles City, Montana (111°F and 115°F, respectively), and Sheridan, Wyoming (109°F), recorded new all-time highs on July 12. Each of these stations beat their previous record by at least 2°F, and Miles City broke its record by 4°F. Montana records date back to the 1930s; Sheridan’s record begins in 1907.

Several locations in Utah also broke all-time records, 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 dating back to the 1890s.

Extreme heat doesn’t just make people uncomfortable. It can have serious health consequences, especially 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 increased tenfold during the July heat.

Heat waves like this 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), a 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 eastward 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 is not the only country facing significant heat. Parts of Western Europe, Central Asia and East Asia are also facing heat waves.

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

• AccuWeather (2026, July 13) ‘Steam cooker’ pattern takes hold over the center and east as heat and humidity peak. Accessed July 14, 2026.
• NASA (2025, May 8) Increase in heat waves in North America over the past 40 years. Accessed July 14, 2026.
• NASA Earth Observatory (June 9, 2010) GEOS-5: A high-resolution global atmospheric model. Accessed July 14, 2026.
• National Weather Service (2026, July 14) Short-term forecast. Accessed July 14, 2026.
• NOAA (2026, July 12) Record heat in southern Montana July 12, 2026. Accessed July 14, 2026.
• Royal Meteorological Society (2021, August 11) What is a heat dome? Accessed July 14, 2026.
• US Centers for Disease Control and Prevention (2026) Everyday Heat-Related Illnesses. Accessed July 14, 2026.
• US National Weather Service, via Facebook (2026, July 13) Yesterday was pretty historic in terms of heat. Accessed July 14, 2026.
• Washington Post (2026, July 14) One of the strongest heat domes on the planet will soon scorch the East Coast. Accessed July 14, 2026.