Smoke plumes from large wildfires like the Bridge fire can create an added obstacle in fighting their spread — their own independent weather events.
The Bridge fire, which as of Wednesday, Sept. 11, had burned more than 47,000 acres with 0% containment, is being described as having plume dominated fire behavior. The fire started Sunday, Sept. 8, leading to evacuations in Wrightwood and Mount Baldy.
Bryan Lewis, a meteorologist at the National Weather Service Los Angeles/Oxnard office, said large smoke plumes from wildfires don’t just impact air quality and visibility. He said smoke rises and condenses to form clouds, sometimes referred to as pyrocumulus clouds.
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“One of the major concerns with that is the downdraft that comes off of it similar to a thunderstorm,” Lewis said.
This is caused by rising air that gets capped by smoke and forced down toward the surface creating gusty winds, he said.
“Those winds can essentially go in any direction which makes it extremely dangerous in terms of fire growth at the surface,” Lewis said.
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He said that on Sunday this phenomenon created about 50 mph winds. While clouds caused by smoke look similar to thunderstorm clouds, Lewis said, it is rare that they result in rain and lightning.
“The higher that plume can grow is essentially what correlates to stronger winds at the surface,” Lewis said.
Lightning strikes are exactly what happened as a result of the plumes from another Southern California fire over the weekend. The raging Line fire had burned 34,659 acres by Wednesday, Sept. 11. The fire started on Thursday, Sept. 5.
The fire was so intense on Saturday that it created its own storm clouds. The National Weather Service recorded thousands of lightning strikes, including over 280 ground strikes.
Those thunderstorms and lightning strikes created “havoc” for firefighters, according to Cal Fire spokesman Rick Carhart.
“They’ll get wind shifts that just happen in a matter of moments,” he said.
Lisa Cox, public information officer with the California Interagency Incident Management Team 5, which is assigned to the Bridge fire, said plume dominated fires like the Bridge fire lead to a high potential for throwing spot fires ahead of the head of the fire.
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“There’s several things coming into alignment to create that extreme fire behavior,” Cox said. “One of them is you need oxygen, you need fuel and you need ignition.”
She said the oxygen comes from winds that don’t have to be at high speeds to create these types of events. Operations and fire behavior personnel have not reported any lightning created by the smoke plumes on the Bridge fire, Cox said.
Crews are expecting one change in weather Wednesday afternoon on the southern end of the fire that will help containment.
“There’s going to be actually a slight increase in humidity this afternoon so that’s good news and that’s really going to help firefighters secure containment lines we have to the south that threaten communities below it in L.A.,” Cox said.
Reporter Beau Yarbrough contributed to this report.
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