What is a heat dome? The climate phenomenon behind record heat

Summer is officially here, and it’s kicking off with an extreme heat dome that’s scorching much of the Central and Eastern United States. 

“A strong upper-level ridge parked over the eastern half of the country will continue to generate an extremely dangerous heat wave this week,” the National Oceanic and Atmospheric Administration’s National Weather Service warns. 

High temperatures in the 100s are expected to break records, as will overnight lows dipping only into the 70s or low 80s and providing little relief. And the humidity increases the threat with heat indexes reaching near 115 degrees in some areas. 

Here’s what causes heat domes, how climate change may be fueling them, and what you can do to protect yourself from extreme heat.   

A heat dome is a meteorological phenomenon produced when a large area of high pressure in the atmosphere forms a ridge over a region and stays there for days or even weeks.   

“This ‘dome’ acts like a lid, preventing heat from escaping and blocking cloud formation, which leads to persistently high temperatures and minimal relief from the heat,” explains AccuWeather Meteorologist Brandon Buckingham.

When hot air attempts to rise it’s blocked by the high-pressure ridge. As it sinks, it compresses and grows steadily hotter, producing conditions of extreme heat near the surface over areas hundreds of miles in size.  

These oppressive heat events are nothing new. However, the term “heat dome,” which isn’t a formal scientific term, has become a popular way to describe the phenomenon in recent years. 

What causes heat domes? 

Unlike a heat wave, in which various factors might cause hot weather, it takes specific weather conditions to create a heat dome.  

A heat dome is typically driven by a change in atmospheric patterns. When patterns disrupt the flow of the jet stream—the aerial river of strong, fast-flowing winds that swerve across the continent from west to east in a wavy pattern—areas can experience extreme weather patterns, such as heat waves, floods, cold spells, storms and droughts. When a jet stream’s north and south loops become too big, they slow or stagnate, stalling the high-pressure system that then forms the top of the heat dome.  

(Heat waves kill people. Here’s how climate change is making it much worse.)

 Ocean climate patterns, including La Niña, can help lay the groundwork for a heat dome when warmer-than-usual sea surface temperatures alter these patterns of air flow. 

The high-pressure system prevents warm air from rising, stifling cloud formation and creating persistent sunny and dry weather. As more solar radiation reaches the surface, the more heat it pours into the dome. 

How do heat domes move?

Unfortunately for those experiencing them, heat domes tend to be stagnant or move slowly, squatting over large areas. Their course and duration are generally steered by patterns of atmospheric circulation, and particularly, the jet stream. 

“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,” Buckingham says. “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.” 

How is climate change impacting heat domes?

The Intergovernmental Panel on Climate Change’s Climate Change 2023 Synthesis Report finds, “It is virtually certain that hot extremes (including heatwaves) have become more frequent and more intense across most land regions since the 1950s.” 

Heat domes are among those heat events. As warmer ocean and land temperatures provide a higher baseline, the warming effects of a heat dome are amplified. Also, less cooling evaporation can occur as soil moisture dries out with heat and drought.

(Here are 10 practical ways to manage extreme heat.)

Climate change may also be altering jet stream behaviors that contribute to heat domes. “Changes in atmospheric circulation—linked to warming in the Arctic—can lead to more stagnant weather patterns that allow heat domes to persist,” explains Ashley Ward, director of the Heat Policy Innovation Hub at Duke University. 

Not only are heat domes more common, but they are also lasting longer. Some, like the 2021 heat wave in the Pacific Northwest, smashed so many records that they are altering scientists’ understanding of extreme heat in a changing world.  

How do heat and humidity impact the body?

The hot, sticky conditions in a heat dome are more than just uncomfortable. 

“Heat and humidity together pose serious health risks,” says Mostafijur Rahman of Tulane University, who studies the effects of extreme weather on human health.

These conditions stifle the body’s primary cooling system—sweat. The body cools down when sweat evaporates off the skin, but high moisture content in the air means sweat can’t vaporize as efficiently, which leads to rising core temperature. 

(Here’s what extreme heat does to the body.)

“This can result in dehydration, heat exhaustion, and potentially life-threatening heat stroke” Rahman adds. “The health risks are particularly high for older adults, children, individuals with chronic conditions, and people who work outdoors.” 

How can you stay cool in a heat dome?

According to the Environmental Protection Agency, more than 1,300 deaths per year in the United States are due to extreme heat. To stay safe, it’s important to stay hydrated, avoid outdoor activity during peak heat, and seek out cool environments. 

Creative cooling techniques include using fans, taking cold showers, and immersing your feet and ankles, or your arms to the elbows, in cold water. Wiping down your skin with a cool washcloth, while sitting in front of a fan, can also effectively lower your core body temperature. 

(How to stay cool and comfortable in a heat wave.) 

“When temperatures reach certain levels outside, the only way to be safe is to seek out air conditioning,” Ward says. 

If you’re not in an air-conditioned space, she recommends making a heat action plan. Locate cooling centers in your area and note their hours of operation. Also, think of informal cooling spaces, like shopping malls or a friend’s home, where you can beat the heat. 

“Most importantly, pay attention [to your body],” Ward stresses. “Seek help immediately if you show signs of heat stroke, and check on family, friends, and neighbors who are vulnerable.”