As if they aren’t already facing enough, firefighters in California also could encounter fire tornadoes — a rare but dangerous phenomenon in which wildfires create their own weather.

The National Weather Service warned on Tuesday that the combination of high winds and severely dry conditions have created a “particularly dangerous situation” in which any new fire could explode in size. The advisory, which runs into Wednesday, didn’t mention tornadoes, but meteorologist Todd Hall said they’re possible given the extreme conditions.

Fire whirl, fire devil, fire tornado or even firenado — scientists, firefighters and regular folks use multiple terms to describe similar phenomena, and they don’t always agree on what’s what. Some say fire whirls are formed only by heat, while fire tornados involve clouds generated by the fire itself.

The National Wildfire Coordinating Group’s glossary of wildland fire terms doesn’t include an entry for fire tornado, but it defines a fire whirl as a “spinning vortex column of ascending hot air and gases rising from a fire and carrying aloft smoke, debris and flame,” and says large whirls “have the intensity of a small tornado”.

Wildfires with turbulent plumes can produce clouds that in turn can produce lightning or a vortex of ash, smoke and flames, said Leila Carvalho, professor of meteorology and climatology at the University of California. “There is a rotation caused by very strong wind shear and a very hot, localised low-pressure system,” she said.

Fire tornados can make fires stronger by sucking up air, Carvalho said. “It creates a tornado track, and wherever this goes, the destruction is like any other tornado.”

In 2018, a fire tornado the size of three football fields killed a firefighter as it exploded in what already was a vast and devastating wildfire near near Redding, about 400 km north of San Francisco in northern California. Scientists later described an ice-capped cloud that reached 11 km into the air and caused winds up to 230 kmph.