Northern California was alerted to a rare tornado warning unlike any other by the National Weather Service - a fire tornado.
Sure enough, a fiery tornado was spotted shortly after the warning on Saturday near the Nevada border, where a large wildfire, winds and extreme temperatures combined to create a dangerous storm.
The Reno office of the National Weather Service knew the mixture of 60-mph winds with pyrocumulonimbus clouds from the Loyalton Wildfire could produce a fire-induced tornado. The forecasters warned the conditions posed "an extremely dangerous situation for firefighters."
"The Loyalton Fire to the east of the Sierra Valley exploded most impressively this afternoon, with a very large pyrocumulus and reports of fire tornadoes," the NWS warning said. "Due to the possibility of very strong fire-generated winds and extreme fire behavior with danger to fire personnel, a tornado warning was issued to heighten awareness in the area of the fire."
The wildfire has charred 20,000 acres in Lassen County, California, as of Sunday morning and has ignited serious concerns and sparked evacuations on Saturday for portions of Sierra, Lassen and Plumas counties.
Firenados are created when rising hot air from a fire becomes twisted by winds changing direction, much like the more common land tornado. The difference between a regular tornado and the firenado, however, is that winds combine with smoke plums to create especially dangerous conditions.
"In terms of the ingredients, the intense heat of wildfires already causes large, billowing columns of rising hot air and smoke, but what causes them to turn into "pyrocumulonimbus", or thunderstorm clouds caused by wildfire smoke, has to do with the state of the atmosphere above the fire," said AccuWeather Meteorologist Jake Sojda.
Typically in the west, the air is very dry, so the air simply doesn't have enough moisture for the rising air above the fire to turn into clouds, you just see all of the ash and embers and dust from the wildfire itself. But Sojda explained that if the atmosphere above a wildfire gets an influx of moisture, then the rising air and smoke can also form clouds as it rises and cools.
"A storm system off the California coast helped push some extra moisture into Northern California, enough to allow the rising air and smoke from the Loyalton Fire to turn into clouds and eventually a towering thunderstorm," Sojda said.
"Localized wind currents caused by a combination of the thunderstorm, the intense heat from the fire, and the shape of the valley around the fire and storm helped cause the storm to rotate, just like a supercell thunderstorm that are famous for causing tornados in places like the Great Plains," Sojda said.
Sojda warns, this poses an extreme danger.
"Not only can these "pyro-thunderstorms" cause wind damage and tornadoes just like a more traditional severe thunderstorm, but they can also cause the fire to behave very erratically and spread very quickly. Embers blown about by the gusty thunderstorm winds can also start new fires. Since it is a thunderstorm, there is also the threat of lightning, which can start new fires, but can also be dangerous to firefighters without shelter who are trying to fight the fire," Sojda said.
AccuWeather Senior Meteorologist and western U.S. blogger Brian Thompson said small whirls of fire are common in wildfires, but vortices as large as fire tornadoes are very rare. The most recent fire tornado to cause massive damage in the United States was in Redding, California, in 2018. It was equivalent to an EF3 tornado with winds reaching 143 mph and killed five people.
"A fire tornado looks somewhat like a fire whirl, which is a rotating column of flames," he said. "However, in these larger fire tornadoes, the stronger circulation draws in more smoke from the surrounding areas, so it can appear to look more like a tornado associated with severe weather, with the smoke mimicking what an actual tornado looks like."
In addition, the presence of a fire tornado can help the wildfire to spread faster.
"Whether the whirl of flames moves out of the burn area, or the embers from the fire get pulled into the fire whirl and then dispersed outside of the fire, both can help a wildfire spread quickly," he said.
By Saturday afternoon, the immediate threat for tornado activity decreased, but the National Weather Service Reno warned that throughout the evening "extreme fire behavior" would continue in Loyalton in the form of new fire tornadoes and 60-mph gusts. They alerted individuals to stay away from the area.
According to Sojda, conditions are expected to remain conducive for these types of "fire thunderstorms" from Northern California into the northwestern U.S., into the middle of the week as atmospheric moisture will remain relatively high and a series of disturbances push across the region. However, it may also provide the opportunity for some thunderstorms to aid firefighters by bringing some localized downpours.
The cause of the fire still remains unknown, according to inciweb.gov.
In Southern California, brush fires prompted mandatory evacuations near Los Angeles. The Lake Fire exploded to 10,000 acres within a matter of hours after igniting on Wednesday afternoon. During Wednesday night, it spread across another 500 acres, the Los Angeles County Fire Department announced. As of early Sunday monring, the fire has scorched more than 17,800 acres of land.
At least 100 structures were within the evacuation zone, David Richardson, Jr., chief deputy of emergency operations with the Los Angeles County Fire Department, told reporters.
The county fire department noted 5,420 structures are threatened by the fire. Over 1,000 personnel are assigned to the fire with three helicopters and 173 engines.
The wind and humidity level will also be aiding the fire in putting up a fight this week.
"Current modeling suggests the wind in the vicinity of the fire each of the next couple of afternoons will be out of the southwest in the 10- to 20-mph range and taking the smoke into the Antelope Valley," AccuWeather Senior Meteorologist John Feerick said. "At night, the wind switches more out of the northwesterly direction off the Tehachapi Mountains, and that switch in wind direction could cause major problems in fighting this fire. We also know that in the vicinity of fires the wind can be much stronger and switch on a dime to begin with."
Humidity levels are also expected to drop this week, Feerick said, adding to the challenges to contain the erratic blaze.