Why is it so…
Why is it so hot?
Usually because a big area of high pressure has parked over you. Air inside it sinks and warms, clouds can't form, and the sun bakes the ground a little more each day. Meteorologists call a strong one a heat dome.
High pressuresinking, warming air
Dry groundheats faster
121°FLytton, BC, 2021 heat dome
Show me why1 min
The lid on the pot
High pressure means air slowly sinking from high up. Sinking air is squeezed and warms, about 5.5°F for every 1,000 feet it drops, and it dries out, so clouds and storms are suppressed. Under a strong, slow-moving high the same air sits over you for days, soaking up sunshine and getting hotter each afternoon.
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Why it builds day after day
- Dry ground heats faster. When soil is moist, a lot of the sun's energy goes into evaporating water. Once it dries out, that energy heats the air instead.
- Nights stop cooling. Warm air, cities and humid air hold heat overnight, so each day starts warmer than the last.
- It barely moves. Heat domes are often blocked by the jet stream bending around them, so they can stall for a week or more.
Where your heat came from
Not all heat is home-grown. Some days the wind delivers it: desert air in a Santa Ana, or hot, humid air from the Gulf in the South. Air Story traces your air back three days so you can tell the difference.
Questions people ask
- What is a heat dome?
- A strong, persistent area of high pressure high in the atmosphere. Sinking air under it warms and clears the sky, trapping heat over a region for days.
- How hot can a heat dome get?
- Extremely: in June 2021 a heat dome pushed Lytton, British Columbia to 121°F, a Canadian record.