Heat Dome vs Heatwave: Key differences explained and why they matter

As scorching temperatures grip large parts of the world, terms such as heat dome and heatwave have become increasingly common in weather reports. While they are often used interchangeably, they describe different aspects of an extreme heat event.

What is a heat dome?

According to the American Meteorological Society (AMS) Glossary of Meteorology, a heat dome is "an exceptionally warm air mass at middle latitudes during the warm season that is associated with a synoptic-scale area of high pressure aloft." The AMS explains that the sinking air associated with the high-pressure system undergoes compressional warming, while stagnant atmospheric conditions help the warm air mass remain in place.

In simple terms, a heat dome is the atmospheric setup that allows heat to build and persist over a region.

What is a heatwave?

While a heat dome refers to a weather pattern, a heatwave describes the extreme heat experienced on the ground.

According to the World Meteorological Organization (WMO), a heatwave is "a period of statistically unusual hot weather persisting for a number of days and nights." The WMO notes that there is no universal definition because heatwave thresholds vary according to local climate and historical temperature records.

Similarly, the US National Oceanic and Atmospheric Administration (NOAA) defines a heatwave as "a period of unusually hot weather that typically lasts two or more days."

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Heat dome vs heatwave: What's the difference?

The distinction lies in cause versus outcome.

According to NOAA, a heatwave is the prolonged spell of unusually hot weather experienced at the Earth's surface, while a heat dome is the persistent high-pressure system that traps warm air and allows temperatures to build over time. NOAA says the high-pressure system acts like a lid, preventing warm air from rising and limiting the movement of cooler air into the affected region.

The American Meteorological Society similarly describes a heat dome as an atmospheric feature—a warm air mass associated with high pressure aloft—rather than the heat event itself.

How does a heat dome form?

Understanding how a heat dome forms helps explain why some heatwaves become exceptionally intense and long-lasting.

According to NOAA, heat domes develop when a strong high-pressure system settles over a region. The system forces air downward, where it warms through compression, while also suppressing cloud formation. With fewer clouds, more solar radiation reaches the ground, allowing temperatures to keep rising. Because the high-pressure system blocks cooler weather systems from moving in, the accumulated heat can persist for days.

NASA adds that these high-pressure systems can become stationary when the jet stream slows or develops large bends, allowing hot air to remain trapped over the same region for an extended period.

Can a heat dome cause a heatwave?

According to NOAA, persistent high-pressure systems are among the primary weather patterns responsible for prolonged periods of extreme heat. By blocking cooler air masses and storm systems, they allow temperatures to remain well above normal for several consecutive days, creating the conditions for a severe heatwave.

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However, the World Meteorological Organization notes that heatwaves can also develop under other atmospheric conditions depending on regional weather patterns. In other words, while heat domes are a major driver of many extreme heat events, they are not the only mechanism behind heatwaves.

Why are heat domes and heatwaves becoming more common?

Scientists say a warming climate is increasing the likelihood of extreme heat events.

According to the Intergovernmental Panel on Climate Change (IPCC), it is "virtually certain" that the frequency and intensity of hot extremes, including heatwaves, have increased across most land regions since the 1950s because of human influence. The IPCC also projects that additional global warming will make extreme heat events more frequent and more intense.

NASA says rising greenhouse gas concentrations are increasing average global temperatures, making naturally occurring weather patterns, including persistent high-pressure systems, capable of producing hotter and longer-lasting heatwaves than in the past.