What Is a Heat Dome? The Weather Phenomenon, Explained

Summertime is generally associated with warm days and sunshine. This type of weather is part of what makes this season so beloved, but sometimes summer temperatures can creep far beyond the realm of bearability, reaching highs that make you want nothing more than to douse yourself in an ice bath after only a minute outdoors. 

Extreme heat poses many risks to both physical and mental health. Fortunately, there are precautions you can take and ways to cope with excessive temperatures. 

In the meantime, as you sweat buckets or seek refuge from extreme heat, you may be wondering what causes heat spikes. You may also have heard the term “heat dome,” which describes a phenomenon behind extremely high temperatures occurring everywhere from Houston to Spain in the summer of 2026. Here’s what to know about this dangerous weather event.

What Is a Heat Dome?

Heat domes are generally said to occur when high pressure systems move into the atmosphere and trap heat, causing the air below them to heat up further. This can result in extremely hot temperatures that can last for up to weeks at a time.

One way to understand this phenomenon is to imagine how a lid on a pot traps heat, causing water to boil. “You can actually repeat this process on a small scale,” Greg Carbin, forecast operations chief at the National Weather Service’s Weather Prediction Center, told The New York Times. “When you’re inflating a flat tire, as the air goes in and the pressure builds, the molecules move faster, they are closer together, and they heat up.”

Typically, heat domes cause the ground to warm and lose moisture, leading to even higher temperatures. Heat domes also generally reduce cloud cover and rain, allowing more sunlight to reach the Earth and further causing temperatures to rise.

A particularly devastating heat dome occurred in the Pacific Northwest in 2021, when temperatures rose above 100 degrees Fahrenheit for over 27 days and resulted in the deaths of hundreds of people. 

This helped lead to increased research on heat domes. In 2022, the American Meteorological Society added the term to its index, defining a heat dome as “an exceptionally hot air mass that develops when high pressure aloft prevents warm air below from rising, thus trapping the warm air as if it were in a dome.”

Are Heat Domes the Same as Heat Waves?

Meteorologists and scientists disagree on exactly what constitutes a heat dome. Many experts agree that all heat domes cause heat waves, but not all heat waves result from heat domes. According to Yale Climate Connections, heat waves are indeed often caused by heat domes, but not all heat waves involve dome-like atmospheric conditions. 

However, some experts aren’t fans of the term “heat dome” due to the fact that it is often confused with heat waves, among other reasons. Many prefer to avoid confusion by omitting the term entirely and simply using “heat wave” to describe any extended period of high heat.

What Causes Heat Domes?

Jet streams are narrow bands of strong winds in the upper atmosphere. They are driven by Earth’s rotation and the movement of air away from the equator. Heat domes occur when these jet streams stall or stagnate, causing a buildup of pressure. 

“The positioning of the jet stream often determines how long a region will suffer under the dome and whether cooler air from higher latitudes can move in,” AccuWeather Meteorologist Brandon Buckingham told National Geographic. “When the jet stream shifts or weakens, the dome may expand in size or move into new areas. Relief finally arrives when the ridge of high-pressure breaks down, causing the dome to dissipate quickly.” 

Many experts say that heat domes have been occurring with increasing frequency in recent years due to human-caused climate change. According to the Intergovernmental Panel on Climate Change's 2023 Synthesis Report, “It is virtually certain that hot extremes (including heatwaves) have become more frequent and more intense across most land regions since the 1950s.” 

What Should You Do During a Heat Dome?

In general, staying hydrated and indoors in an air-conditioned environment is the best way to wait out a heat dome.

If you don’t have access to air conditioning, it’s a good idea to locate a nearby air-conditioned cooling center in the case of a heat wave or heat dome. Additionally, cooling techniques like taking a lukewarm shower, wiping your skin with a cool washcloth, and using fans can help. 

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