California is on fire: What are fire whirls, fire tornadoes, fire clouds and running crown fires?

Fire tornadoes may seem appropriately apocalyptic, given a year full of terrifying events.

The fire tornado, or “extreme fire activity,” brought on by the Loyalton Fire raging now in Northern California, has blazed through nearly 50,000 acres of land, and just over a third of it is contained.

The Loyalton Fire is among the 367 wildfires California is facing, 23 of which are considered major. The number is likely to rise amid a confluence of sweltering heat and lightning storms, said California Gov. Gavin Newsom in a news conference Wednesday.

Heath Hockenberry, the National Weather Service's national fire weather program manager, told USA TODAY that fire whirls and "firenadoes" – terms for the same phenomenon – are among the more dangerous elements firefighters have to face.

"They’re one of the most dangerous fire behavior phenomenon and every firefighter is aware of them," he told USA TODAY. "You just have to stand back and let it run its course and fight when you can engage again."

Other fire weather events can hamper firefighters. Here are some examples:

What is a fire tornado? 'Extreme fire activity' sparks rare weather warning at Loyalton Fire near Reno

Pyrocumulus clouds

One of the more distressing examples are pyrocumulus clouds – essentially “fire clouds” that form over heat sources. The bushfires that ravaged Australia earlier this year featured the massive clouds.

“They’re very concerning for firefighters because they cause their own storm,” he said. 

In humid climates, reported ABC News, they are able to generate rain and provide some relief for storms. But in drier climates, the lightning from the storm itself can ignite more fires.

A distressing effect of pyrocumulus clouds is “spotting,” Hockenberry said.

“It’s not as shiny” a name as a "firenado," Hockenberry points out, but it’s as frightening to firefighters as their fire swirl brethren.

Essentially, it is “when embers that are on fire spew out from the clouds” outside the fire location, causing fires to form in areas as far as several miles away from the main zone.

Running crown fires

Two separate fire events – running fires and crown fires – also can merge to form what are known as running crown fires. 

Running fires are when fires accelerate at a rate faster that can be controlled. Crown fires take place when fires climb a tree; they usually spread below the tree line before making their way upward, Hockenberry says.

Running crown fires make their way to the tops of trees and move quickly. Also known as active crown fires, these fires appear to burn through the entire canopy as opposed to individual trees, according to the USDA Forest Service.

“You can almost watch tree to tree burn in a matter of seconds from each other,” Hockenberry said, “and you’ll see this gigantic flame wall spreading on the tops of trees.”

Fire tornadoes, whirls

Fire tornadoes, such as the one in the Loyalton Fire, are generated when intense heat from a wildfire causes hot air to rush up from the ground.

All of the air rushing upward has to be replaced at the surface, said Dawn Johnson, a senior meteorologist at NWS Reno to USA TODAY earlier this week. As air comes in it sometimes starts to rotate. 

But fire whirls, as scary as they are, have historical precedent. The Great Chicago Fire in 1871, one of the most devastating in American history, was exacerbated by fire whirls.

There are plenty of others, too, said Hockenberry, both recently and in the past, including the 2018 Carr fires, a 1923 earthquake in the Kantō region of Japan that caused severe fires, and the Peshtigo Fire in Wisconsin, which erupted at the same time as the Great Chicago Fire.

While firefighters have to grapple with these every wildfire season, Hockenberry makes it a point to note that fire tornadoes – and other alarming fire weather phenomena – aren't spiking drastically because of climate change or other factors.

"Longer, drier fire seasons mean more fires, so there is an increased opportunity for them to form," he said. "But it’s not like regular tornadoes – they have to have a heat source that’s the right shape, they have to have a fire in the right terrain, wind flow that’s just right – so you’re not going to see a rash of fire tornadoes.

"The opportunity for them to form in the right conditions is a low likelihood and rare."

Contributing: Jordan Culver, Doyle Rice and Elinor Aspegren, USA TODAY; Scott Linesburgh, The Record (Stockton, Calif.); and Reno-Gazette Journal staff writers