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Fire Clouds Are As Terrifying As They Sound

A massive white and gray cloud rises over hills, with palm trees in the foreground.
A pyrocumulus ash plume towers above Banning, California during the Apple fire on August 1, 2020.
AFP via Getty Images)
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Intimidating. Ominous. Apocalyptic.

All adjectives fair to use when describing fire clouds, known in scientific circles as pyrocumulus or flammegenitus.

Those massive clouds, some have noted, have a distinctive nuclear vibe. And if you see one, there's reason to be alarmed.

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Rare pyrocumulus clouds have been churning high above the Idyllwild hellscape, bringing with them strong winds, the threat of lightning and turbulence that can make it difficult for aircraft to help firefighters on the ground.

"If it weren't so dangerous on the ground we could all go, 'Damn, that is so cool,'" said Char Miller, professor of environmental analysis and history at Pomona College.

As fire spreads, intense heat causes a rush of hot air and particulate matter to rise. When that giant mass of air hits the atmosphere and mixes with cooler, moist air, flammagenitus, or fire clouds, are created.

When they arrive things can get a lot worse.

  • Lightning can start fires in new areas
  • Winds act as bellows and push fire in all sorts of directions

And, as if that weren't bad enough, the super-heated air pulls embers from the ground and deposits them for miles. Meaning, they can rain down little pieces of fire on dry trees and shrubs that haven't started burning yet.
"It is producing its own weather because it is so big and it's so powerful," said Miller.

The clouds are usually visible above wildfires and volcanic eruptions. Places where extremely hot air on the surface rises to meet cooler air above.

They'll flatten when firefighters manage to squelch the fire, or if temperatures drop significantly.

There's rain in the forecast this weekend, though it looks like much of the Southwestern U.S. will suffer under a heat dome for the coming weeks. High temperatures, decreased humidity and high winds will remain constant, meaning perfect fire weather will continue to threaten much of the region.


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