Scientists Are Learning More About Fire Tornadoes, The Spinning Funnels Of Flame

MARY LOUISE KELLY, HOST:

Climate change is driving longer and more intense wildfire seasons. That has been proven. It is also known that when fires get big enough, they can create their own weather, which can include so-called fire tornadoes. What's unknown is how common extreme phenomena like fire tornadoes are. Montana Public Radio's Nick Mott checked in on the state of the science.

NICK MOTT, BYLINE: As hundreds of wildfires have broken out across the country this year, lots of people have been seeing videos like this one from the over 10,000-acre Tennant Fire in Northern California that was posted on Facebook in late June.

(SOUNDBITE OF WIND BLOWING)

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MOTT: It's a funnel cloud, like the kind that form tornadoes or, more commonly, dust devils. But this one is a swirl of smoke and flame. It's pretty dramatic and scary-looking in the video as it approaches fire engines, heavy machinery and a hotel sign swaying in the wind.

(SOUNDBITE OF WIND BLOWING)

MOTT: Jason Forthofer, a firefighter and mechanical engineer at the U.S. Forest Service's Missoula Fire Sciences Lab in Montana, says funnels like this one, which is large enough to do some damage, are called fire whirls.

JASON FORTHOFER: Fire tornadoes are more of that larger version of a fire whirl, and they are really the size and scale of a regular tornado.

MOTT: It stands to reason that with longer and more intense fire seasons, we're now seeing more fire whirls and fire tornadoes, but...

FORTHOFER: Most likely, it's much easier to document them now because everybody walks around with a camera essentially in their pocket on their phone.

MOTT: He says the data is too young to be sure, but it's plausible more of these are happening as fires grow more intense and the conditions that create them more frequent. The ingredients that create fire whirls are heat, rotating air and conditions that stretch out that rotation along its axis, making it stronger. Forthofer can create them in a chamber in the lab here. He heads toward an empty 12-foot-tall tube. He puts alcohol into its bottom to prepare it to catch flame.

FORTHOFER: So we'll just pour about...

(SOUNDBITE OF LIQUID POURING)

FORTHOFER: ...Maybe a cup and a half or so.

MOTT: He finds a lighter to get the flames going.

FORTHOFER: So we're going to start that.

(SOUNDBITE OF HISSING, BANG, WIND BLOWING)

MOTT: A spinning funnel of fire about a foot in diameter shoots upward through the tube.

(SOUNDBITE OF WIND BLOWING)

MOTT: In the real world, it's hard to say how frequently fire whirls or tornadoes happened in the past since they often occur in remote areas with no one around, but Forthofer went looking for them. He found evidence of fire tornadoes as far back as 1871, when catastrophic fires hit Chicago and Wisconsin.

FORTHOFER: I realized that these giant tornado-sized fire whirls, let's call them, happen more frequently than we thought. And a lot of firefighters didn't even realize that that was even a thing, that that was even possible.

JULIE MALINGOWSKI: They are rare, but they can happen.

MOTT: Meteorologist Julie Malingowski gives firefighters weather updates on the ground during wildfires. That can be life or death information. She says the most important factors day to day are more mundane, like heat, wind and relative humidity.

MALINGOWSKI: Everything the fire does as far as spread, as soon as a fire breaks out, is reliant on what the weather's doing around it.

MOTT: And researchers are tracking other extreme weather behavior produced by fires, like fire-generated thunderstorms from what are called pyrocumulonimbus clouds, or pyroCBs. They can produce dangerous conditions, including those necessary for fire tornadoes to occur. Michael Fromm is a meteorologist at the Naval Research Lab in Washington, D.C. He says the data set only goes back less than a decade, but...

MICHAEL FROMM: In terms of the head count of pyroCBs this season, it's already achieved a number, I think, that exceeds what we've seen in the past. And the fire season isn't even over yet.

MOTT: For NPR News, I'm Nick Mott in Montana.

(SOUNDBITE OF VOLSKY'S "BETWEEN SPHERES") Transcript provided by NPR, Copyright NPR.