What is a heat dome?
A heat dome is a large area of high pressure that sits over a region for days or weeks. The air in it slowly sinks, gets squeezed and warms up, and it pushes clouds away so the sun heats the ground nonstop. Like a lid on a pot, it traps the hot air underneath.
High pressure parks over a region
Sometimes the jet stream, the fast wind high up, gets stuck in a big wave. A zone of high pressure then stays in place over the same region instead of moving on, sometimes for a week or more.
Share this stepSinking air works like a lid
Inside the high pressure, air slowly sinks. As it sinks it gets squeezed and warms up, like air in a bike pump. It also blocks clouds from forming, so the sun shines all day.
Share this stepThe heat builds day after day
The ground and buildings heat up during the day, but the hot air can’t rise and escape. Nights stay warm, and each day starts hotter than the last. Cities get it worst, because asphalt and stone store heat.
Share this stepA lid of sinking air over a heating pot.
High pressuresinking airtrapped heat
Heat domes are normal weather patterns, but as the climate warms they start from a higher temperature, so heat waves become hotter and more common. Heat is one of the deadliest kinds of weather.
Common follow-up questions
How long does a heat dome last?
Usually from several days to a couple of weeks, until the jet stream shifts and moves the high pressure away.
Why are nights so warm during a heat dome?
The ground, buildings and air stay hot, and without clouds or wind changes, heat can’t leave fast enough overnight.
How do I stay safe in extreme heat?
Drink water often, stay in the shade or cool rooms during the hottest hours and check on elderly people, small children and people who are ill. Get help if someone becomes confused or stops sweating.
Is a heat dome caused by climate change?
Heat domes have always happened, but a warmer climate makes them hotter and more frequent, according to climate researchers.
