LOS ANGELES -- A massive wildfire in Northern California spawned rotating columns of flames Saturday, prompting forecasters to issue a rare fire-related tornado warning.
"It was a first for us," said Shane Snyder, meteorologist with the National Weather Service in Reno, which issued the warning shortly before 3 p.m.
Multiple videos posted to social media showed twister-like formations in the path of the Loyalton fire, which started Friday evening in the Tahoe National Forest near California's border with Nevada. The fire quickly grew to 20,000 acres and was 0% contained as of Sunday morning. Authorities were performing updated flight mapping and expected the acreage to rise, said Joe Flannery, public affairs officer for the national forest.
"Our resources on the ground are facing extreme fire behavior, rugged terrain and warm temperatures," Flannery said.
Evan Bentley, severe weather meteorologist with the National Weather Service Storm Prediction Center, wrote on Twitter that radar data showed at least four "distinct anticyclonic circulations" associated with the fire on Saturday. One was present for more than an hour and traveled about four miles, he wrote.
The extreme weather phenomenon is believed to have been sparked by the rapid growth and intensity of the blaze.
"It was hot; it was very unstable atmospherically," Snyder said in an interview, "and that allowed the fire, which is burning very hot and 1/8through3/8 lots of fuel, to really explode up in a vertical sense, up into the atmosphere."
The hotter the air, the more rapidly it rises, he said.
"Hot air wants to rise, and if it's very hot it wants to rise dramatically," Snyder said. "It's allowed to rise because the temperature of the air the fire makes is much warmer than the air around it. So it keeps rising until it's not warmer than the air around it."
That can send a column of smoke up tens of thousands of feet into the atmosphere, he said. And as it rises, the air underneath it needs to be replaced, creating a vortex that pulls in air from all around it.