The tower of billowing cumulus clouds and smoke rising above Northern California’s Carr fire said it all. The flames jumping around Redding’s western edge had created their own micro weather system, tossing fire brands helter-skelter across the baking landscape.
California’s big, destructive wildfires tend to come in two varieties: wind-driven, such as last year’s deadly Santa Rosa conflagration and December’s Thomas fire in Southern California. And what is known as plume-dominated, when a fire’s plume of smoke and ash is big and hot enough to exert control.
Wind gusts were a factor in the Carr, which destroyed 65 residences on Redding’s edge, sent panicked homeowners fleeing in the middle of the night and caused the deaths of a city firefighter and a bulldozer operator. But fire experts say the explosive growth of the Carr was more a function of extreme heat and dried-out fuels that stoked flames intense enough to generate their own weather.
“This is not what I would call a wind-driven fire,” said U.S. Forest Service meteorologist Tom Rolinski. “It’s more of a plume-dominated fire. It creates a lot of erratic fire behavior.”
The quickly moving blaze jumped the Sacramento River and raced in different directions, creating fire whirls and making it impossible to control. “It was moving all over the place,” said Mike Mohler, deputy communications director for the California Department of Forestry and Fire Protection.
Redding is a city of 90,000 people hugging the Sacramento River on one side and a landscape of oak trees, grasslands and chaparral. Cal Fire officials said the burned homes were outside of town and on the city’s edge — an interface of flammable wildlands and buildings that over the years have been the scene of the state’s deadliest fires.
As is often the case when flames encroach on developed neighborhoods, photos from the Carr fire showed houses in smoldering ruins while nearby trees appeared untouched by flames — evidence that flying embers set the buildings on fire rather than an advancing wall of flames.
While fierce winds that have driven many of the state’s biggest blazes — such as Santa Barbara’s sundowners and Northern California’s diablos — were not a key factor in Redding, other ingredients that fuel big fires were abundant.
Always brutally hot in the summer, the area was hit by record-breaking temperatures this week. Thursday it was 113 degrees.
“The summertime temperatures have been really extreme,” said Dave Sapsis, a state wildfire specialist.
The heat not only sucks the moisture out of live plants, it also further dries out dead limbs and brush. And the combination of the state’s punishing five-year drought, followed by record Northern California rains in 2017, left plenty of fuel. An ignition and the right weather conditions are all that is needed to send flames racing over the hills and up canyons.
Summer in California is wildfire season, but Sapsis said the level of fire activity so far this month, especially in Northern California, is more typical of late August. “The entire northern part of the state has been besieged by fire for about a month now,” he said.
It’s difficult to gauge the effect of climate change on wildfires, as the reasons for more blazes include more human-caused ignitions, a history of fire suppression in the Sierra Nevada and development’s push into formerly empty wildlands.
But scientists say warmer temperatures are a factor in the growth of wildfires in the West.
“I think the warmer temperatures are making them more extreme,” said UC Merced professor Anthony Westerling.
Pyrocumulus clouds — such as the one towering above the Carr blaze Thursday — form when the atmosphere above a fire plume is unstable, usually in the heat of the afternoon.
The collapse of the clouds as temperatures drop at night creates downdrafts that can create dangerous conditions on the ground.