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What Is a Firestorm?

A forest on a hill on fire under a blue sky with dark smoke rising into the air.

The active flame front of the Zaca Fire in Santa Barbara County, CA. This 2007 blaze was one of the largest fires on record in California.
Credit: U.S. Forest Service, photo by John Newman

Weather Forged by Fire

Whether they start from a lightning strike, an unattended campfire, or a downed power line, wildfires can be an incredibly destructive force. Some of them grow so large that they can also create their own weather system.

It's true. At times, a wildfire (or multiple wildfires in the same area) causes a firestorm. That means the heat from the fire creates its own wind system, and this can lead to very strange weather effects.

Cartoon of a boy saying a fire... storm? Yikes!

Fire Wind… and Tornadoes

Firestorms form for two main reasons:

  1. Hot air rises.
  2. Nature hates a vacuum (not the loud cleaning appliance, but an empty space). That means empty spaces don’t stay empty for long.

It all starts because heat is constantly and quickly rising from the fire. As all this heat and air moves upwards, it leaves behind some empty space. Air from all around the fire rushes in to fill that gap. That movement of air creates powerful wind called an updraft.

Illustration of an up arrow with a swirling arrow inside labeled updraft and fire at the bottom of the arrow. There are also two arrows pointing at the bottom of the updraft that say air rushes in.

In some cases, the rising air can be so fast it creates a fire whirl, also known as a fire tornado. Seriously. A tornado of fire. As if a wildfire weren't bad enough by itself!

A fire tornado in brush.

Nothing to see here. It's just a FIRE TORNADO.
Credit: United States Marine Corps.

Cartoon groundhog saying I prefer my tornadoes without fire.

Fire Clouds

As the smoke from the fire rises, it condenses when it reaches the upper atmosphere. The water comes from moisture already in the atmosphere as well as the water evaporating from the burned plants fueling the fire. The cloud that forms is called a pyrocumulus, which means "fire cloud."

Large clouds of smoke with a jet flying in front of them.

A pyrocumulus develops above the Oregon Gulch fire in 2014.
Credit: Oregon Air National Guard, photo by James Haseltine.

If the fire is big enough, it will form a pyrocumulonimbus, or a "fire storm cloud." These can produce lightning, which could set off even more fires. They also generate stronger winds, which fan the fire, making it hotter and helping it spread. No one wants that.

Large smoke clouds in the sky amongst normal clouds.

A pyrocumulonimbus forming in British Columbia, Canada.
Credit: NOAAA, photo by Noriyuki Todo.

Fire Clouds with Occasional Silver Linings

But wait! It's not all bad. Although it’s rare, these fire clouds can also produce rain that helps extinguish the fire. When that happens, it's a wonderful thing.

A cartoon woman saying well, that's some good news!