'A Lid on a Pot': How Does a Heat Dome Work?

A powerful heat dome has settled over the eastern half of the United States this week, pushing temperatures into the 90s and low 100s across much of the region. The National Weather Service warned that when high humidity is added in, it could feel as hot as 105 to 115 degrees in some areas. More than 69 million people from Texas to Maine were under heat alerts on Monday. Officials are urging everyone to take steps to stay safe in the dangerous heat.

In cities like Nashville, Tennessee, temperatures could feel as high as 115 degrees. The local National Weather Service office wrote, 'Mamma mia, it's hot. There's no doubt about it. We're going to be a summer night city all week.' In Iowa, forecasters said the heat index could reach 110 degrees Fahrenheit. Even overnight, there won't be much relief — many areas will only cool down to the mid or upper 70s.

The lack of nighttime cooling makes heat waves more dangerous. When your body can't cool off at night, it stays stressed from the heat for longer. The National Weather Service said this raises the risk of heat-related illnesses, especially for elderly people, young children, and those without air conditioning. People with breathing problems or those taking certain medicines also face higher risk.

So what exactly is a heat dome? Think of it like putting a lid on a pan when you're making a grilled cheese sandwich. Alex Lamers, a meteorologist with the National Weather Service, explained it this way: 'If you've made grilled cheese in a pan and you put a lid on there, it melts the cheese faster because the lid helps trap the heat.' A heat dome works the same way — a large area of high pressure in the upper atmosphere traps warm air near the ground for days or even weeks.

High pressure also usually means dry weather, which makes things even hotter. The heat dome's position is often tied to the jet stream, which is a fast-moving band of wind high in the sky that blows from west to east. When the jet stream bends in a certain way, it can allow high pressure to 'park' over a large area. This can create a feedback loop where the heat keeps building on itself.

Heat domes are not new, but they are becoming more intense because of climate change. Scientists say that burning fossil fuels like coal, oil, and gas warms the planet and makes extreme heat events worse. Both 2023 and 2024 were the hottest years ever recorded, and 2025 ranked as the third hottest. Scientists warn that without action on climate change, we will keep seeing more of these dangerous heat events.

Heat domes have hit different parts of the country in recent years. In 2021, a heat dome caused hundreds of deaths in Oregon and Washington. In 2023, record temperatures stretched from New Orleans to Chicago. In Phoenix, Arizona, there were a record 113 days in a row with temperatures at or above 100 degrees in 2024, and Maricopa County recorded more than 600 heat-related deaths that year.

The heat is not just a problem in the United States. Last week, a heat wave struck Western Europe, with parts of France reaching above 100 degrees. The World Health Organization reported that more than 1,300 extra deaths in Europe since June 21 have been linked to extreme heat. WHO Director-General Tedros Adhanom Ghebreyesus said, 'We were warned,' pointing out that once-rare heat waves are now happening almost every year.

The current heat dome in the U.S. is expected to peak on Thursday or Friday before slowly moving out this weekend. If you have to go outside, doctors say to take lots of breaks and drink plenty of water. Wearing sunscreen and a hat can also help protect you from the sun. Dr. Jess Weisz, a children's doctor in Washington, D.C., says these simple steps can make a big difference in keeping kids and adults safe during extreme heat.