What Is A Heat Dome? Explaining The Deadly Weather Pattern Behind America's Most Dangerous Summer Days

Yahoo

23-06-2025

They're known by many names: Heat dome. Ridge of high pressure. Death ridge. Blocking high.
But do you really know what these are and why they can produce deadly weather?
These expansive bulges of warm air can stretch for 1,000 miles during the spring and summer months and provide sinking air over much of the country.
(MORE: Preparing For The Upcoming Heat Wave: What You Need To Know)
It's that sinking air that is often problematic.
Descending air compresses and warms as it drops closer to the surface. Temperatures can often reach the century mark in the eastern two-thirds of the United States. In the West, these death ridges can push temperatures into the 110s and 120s in the desert.
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Days-long heat waves are often the result.
This sinking, warm air also dries out the ground and the air above it. Thunderstorms have a tough time sprouting due to the suppressive motion of the air. Drought can begin or worsen under ridges of high pressure that last for longer than a week. The air directly under such a system can become still with little to no wind.
During the middle of the summer, this can become a vicious cycle of warming and drying.
These domes can strengthen and expand during this cycle until something comes along to push the high-pressure system elsewhere.
Heat is the No. 1 weather killer in the U.S., with hundreds of fatalities each year. Many of these fatalities occur under heat domes.
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There is one benefit that these domes bring: They can deflect tropical systems away from the United States. They act like a shield for the Gulf Coast or Atlantic seaboard.
While not seen as a benefit, another pattern can emerge on the periphery of death ridges: the ring of fire. No, this isn't the chain of volcanoes that lines the edges of the Pacific Ocean.
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The ring of fire is a curved line or roughly oval-shaped ring of thunderstorms that can encircle a high-pressure system. The thunderstorms are often severe due to the summertime heat and humidity. In June or July, these thunderstorms can become derechos. By later in the summer, if the placement of the ridge is right, the Southwestern monsoon can get a boost.
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Jonathan Belles has been a digital meteorologist for weather.com for 9 years and also assists in the production of videos for The Weather Channel en español. His favorite weather is tropical weather, but also enjoys covering high-impact weather and news stories and winter storms. He's a two-time graduate of Florida State University and a proud graduate of St. Petersburg College.