Heat Domes Are Becoming More Frequent. Here’s What That Means for Summers Across the U.S.

A massive heat dome is forecast to bake the eastern United States in the coming days, with the Southwest already enduring temperatures near 100 degrees Fahrenheit (38 Celsius) this week. By the Fourth of July, dangerous heat could spread across much of the country, putting tens of millions of Americans at elevated risk for heat-related illness.

More than 180 million people across the eastern half of the U.S. fall into Level 3 “major” or Level 4 “extreme” heat risk categories, according to the National Weather Service. Emergency room visits for heat illness spike sharply on those days.

How a heat dome forms

A heat dome is a large, stubborn high-pressure system that parks itself over a region and traps hot, humid air underneath. Warm air flows northward, sinks toward the surface and compresses, which drives pressure and temperatures even higher.

“So what a heat dome really is, is a big high pressure system,” Dr. Erik Nielsen of Texas A&M University told Campus Insights Media. “High pressure systems like this heat dome tend to be in a situation where they’re not moving quite as fast, and so they tend to kind of sit over areas for long periods of time if there’s not another storm system to kind of nudge it out of the way.”

The result is days of dry, sunny weather that pile heat onto the surface and amplify it. In short, heat domes are the engines behind the worst heat waves.

Why this heat dome matters now

The continental U.S. just logged its most abnormally hot March in 132 years of recordkeeping, and forecasters are watching record-shattering extremes ripple out from the Southwest. Extreme heat is also a top concern for the World Cup, which is being co-hosted across the U.S., Canada and Mexico.

Europe is dealing with its own heat dome that began in mid-June, with highs near 40 degrees Celsius (104 Fahrenheit) frying much of the continent. Nielsen said the shock factor matters as much as the raw numbers.

“I think it’s important to understand that places aren’t necessarily prepared for the same sort of weather threats, right? We in the Southern U.S. are used to hot, humid climates. The northern portions of the U.S. are not maybe as used to that,” he told Campus Insights Media.

How to stay safe during a heat dome

Nielsen’s core advice is to plan ahead, especially if extreme heat is unfamiliar in your area.

“So if this is your first time experiencing some of this sort of heat, you really have to kind of go in and plan your day to not be out in the heat of it, because once you’re out and once you’re warm, you’re not going to be able to cool as efficiently, especially if you don’t have a place that has cooled air or that sort of place to come back to,” he said.

Heat domes are especially punishing because nighttime temperatures often stay high, making it harder for the body to recover. Finding cool spaces during both daytime and overnight hours is critical.

The climate connection

Climate scientists say events like this are no longer outliers. Jennifer Francis of the Woodwell Climate Research Center told The Associated Press the trend is unmistakable.

“Heat waves like this are so directly connected to the climate crisis and climate change and it’s because of how we’ve been burning fossil fuels and cutting down forests for so long and increasing the concentration of heat-trapping gasses in the atmosphere,” Francis said.

“These kinds of heat waves and droughts and associated fires are all increasing just as we would expect them to in a warming world,” she added.

The video Extreme European weather — what is a heat dome featuring Texas A&M University instructional associate professor Dr. Erik Nielsen was first published on Campus Insights Media.