Not all meteorologists agree on what distinguishes a fire tornado from a fire whirl. Some say it’s size that sets them apart. Their magnitude can vary considerably; some are no more than a few feet high, whereas others can reach miles into the atmosphere and spin violently enough to rip the roofs from houses, overturn train cars, and rend asphalt from the ground on which it rests. That is to say, they can get rather academic about an especially cataclysmic feature of life on Earth: twisting columns of flames that can whip across the landscape at upwards of 140 miles per hour.
Perhaps the more important point is that whirling pillars of flame are not only common (some experts claim that a ‘nado or whirl will develop in every wildfire, even if people don’t always spot it), they are also known to spread fire faster and less predictably than other conflagrations. So while their naming conventions may vary, scientists and firefighters tend to agree on at least one thing: these frightening sights deserve tremendous respect.
“We’re talking about, really, one of the most extreme sort of phenomenon that you can witness,” says Neil Lareau, an atmospheric scientist at the University of Nevada Reno and an expert in extreme fire behavior. He points to 2018’s devastating Carr Fire in Redding, California, which, in addition to being one of the largest and most destructive fires in that state’s history, generated a swirling spire of flames that extended tens of thousands of feet high. That’s on top of what already sound like apocalyptic conditions. “The sun is almost entirely blotted out by the smoke,” Lareau says. “It’s this hellscape of midnight at noon, and raining fire.”
Lareau classifies the flaming whirlwind in Redding as a true firenado. Like other spinning blazes, it began with updrafts and inflows—the hot air that rises in a column from a fire and the cool air that rushes in at the base of that column to replace it, respectively. But the Carr fire also had shear winds: large air currents, blowing in opposite directions, that produced rotation at their interface. Those opposing winds, combined with the scale of the inferno, whipped the firenado into such a frenzy that it produced its own weather system.
Around the world, fire seasons are becoming longer and more intense. Understanding firenadoes and other spinning fire systems—what shapes they take, how they form and move, and what effect they have on their surroundings—could save money and lives. In the video above, Lareau puts a compelling spin on these subjects in the first installment of a new video series about the science of extreme events.