- Sometimes, wildfires can create their own weather.
- Pyrocumulonimbus are an explosive storm cloud actually created by the smoke and heat from a wildfire.
- Some of the ferocious wildfires this summer in the West have spawned fire whirls.
2021 has been a brutally hot, dry summer in the western U.S., with hundreds of heat records broken amid an unprecedented drought that’s created a tinderbox for ferocious wildfires.
Weather often contributes to the growth and spread of wildfires, with high heat, low humidity, gusty winds and lack of rainfall among the prime culprits. But fires can also influence the weather.
Sometimes, wildfires can create a scary witch’s brew of weather including pyrocumulus clouds, thunderstorms, dry lightning and even fire tornadoes.
Here’s a look at some of the types of weather that wildfires can create:
What are pyrocumulus (‘fire’) clouds?
Pyrocumulus clouds – aka fire clouds – look like giant, dirty-colored thunderheads that sit atop a massive column of smoke coming up from a wildfire. Often the top of the smoke column flattens to take the shape of an anvil.
Here’s how it happens: When air over the fire becomes super-heated, it rises in a large column. As air with more moisture rises, it rushes up the smoke column into the atmosphere, and the moisture condenses into droplets. That’s what creates the “fire clouds” that look much like the thunderheads seen before a big thunderstorm.
Sometimes these clouds can turn even more fierce, becoming what are known as “pyrocumulonimbus” clouds.
A cumulonimbus without the “pyre” part is imposing enough – a massive, anvil-shaped tower of power reaching five miles high, hurling thunderbolts, wind and rain.
Add smoke and fire to the mix and you have pyrocumulonimbus, an explosive storm cloud actually created by the smoke and heat from a wildfire.
NASA has called the these clouds the “fire-breathing dragon of clouds,” in part because they can ravage tens of thousands of acres.
What is dry lightning?
To put it simply, according to the National Severe Storms Laboratory, dry lightning is lightning that hits the ground without nearby rainfall.
How does dry lightning work? Humid air among the clouds feeds thunderstorms, while dry air below causes the rain to evaporate before reaching the ground. Lightning strikes still reach the surface, however, where vegetation is dry from months of persistent heat and low humidity – providing the perfect kindling to ignite a wildfire.
What are fire tornadoes and fire whirls?
Fire whirls, fire tornadoes and “firenadoes” – terms for the same phenomenon – are among the more dangerous elements firefighters have to face as they battle wildfires.
Some of the ferocious wildfires this summer in the West have spawned fire whirls.
A fire whirl is a “spinning vortex column of ascending hot air and gases rising from a fire and carrying aloft smoke, debris, and flame,” according to the Bureau of Land Management’s Glossary of Wildland Fire Terminology. “Fire whirls range in size from less than 1 foot to more than 500 feet in diameter. Large fire whirls have the intensity of a small tornado.”
These fire whirls can form in any size fire, but they are most destructive in large fires. Created by cool air rushing to take the place of hot air, the whirl’s spinning can hurl embers and sparks great distances. Whirls usually intensify a wildfire.
Contributing: The Associated Press