What is a heat dome, and how can it create 'ring of fire' thunderstorms?

As hot weather becomes more common across the United States as summer approaches, some areas will soon experience a heat dome, a phenomenon that acts like nature's oven.

A heat dome is a sprawling area of high pressure that promotes hot and dry conditions for days or weeks at a time.

"Heat domes are a lot like a balloon," AccuWeather Senior Meteorologist Alan Reppert explained. "They expand and contract as the day goes by, and when you are inside of it, it can be a very warm."

Heat domes can also prevent clouds from forming, resulting in abundant sunshine that boosts temperatures, potentially toward record levels.

As temperatures swell, so too does the cooling demand which can increase the strain on the power grid of an entire region. Extended hot and dry spells can also cause drought conditions to develop or worsen.

In late June 2021, a heat dome parked over the West Coast states led to record-shattering temperatures. Seattle hit the 100-degree mark on three consecutive days, peaking at 108 on June 28. It was even hotter in Portland, where the mercury jumped to 116 degrees, melting away the previous all-time record high temperature of 107 set in the city in 1981.

Heat domes can act like large, unmovable bubbles, forcing any moisture to move up and over the bubble of heat. Thunderstorms that ignite on the fringe of the heat dome are known as ring of fire thunderstorms.

"You hear the 'ring of fire' when we talk about volcanoes in the Pacific," AccuWeather Chef On-Air Meteorologist Bernie Rayno explained. "In the world of meteorology, the ring of fire deals with thunderstorms along the northern edges of strong upper-levels high. Oftentimes, this setup produces severe thunderstorms along the northern edges of the heat."

In 2023, AccuWeather unveiled its new heat wave index to help convey the danger of heat waves, including those caused by heat domes.

The AccuWeather HeatWave Counter and Severity Index™ factors in both the length and severity of a heat wave, helping to better inform and prepare people for scorching conditions.

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