The National Weather Service's warning about the “particularly dangerous situation” in which any new fire could explode in size in the Los Angeles area didn’t mention fire tornadoes.

Wildfires tearing through Southern California have already burned tens of thousands of acres and structures down. Now, another threat is facing the area: fire tornadoes.

Wildfires produce a lot of heat, which causes the air above them to rise rapidly. As this hot air moves upward, cooler air from the surrounding area rushes in to replace it. This creates a spinning motion if the surface wind conditions are just right. The result is a vortex, or a spinning column of air.

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 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.