|Above: The massive plume from the Camp Fire, burning in the Feather River Canyon near Paradise, Calif., wafts over the Sacramento Valley as seen from Chico, Calif., on Thursday, Nov. 8, 2018. Image credit: David Little/Chico Enterprise-Record via AP.|
Conditions are ripe for explosive wildfire development over large parts of California from Thursday into Friday. The most immediate threat on Thursday morning was a fast-spreading fire in the Sierra Nevada foothills a few miles east of Chico. Dubbed the Camp Fire, the blaze grew from inception to cover more than 5000 acres in just three hours, according to CAL FIRE. Much of the city of Paradise has been evacuated, and some motorists attempting to leave were reportedly stuck in gridlock.
Incredible #GOES16 satellite imagery of extremely dangerous, fast-moving wildfire in wildland-urban interface currently burning through #Paradise, California at an estimated 80 acres *per minute.* Strong, dry east winds. Really bad feeling about this one. #CampFire #CAwx #CAfire pic.twitter.com/l1667JOmDc— Daniel Swain (@Weather_West) November 8, 2018
Further south, conditions will be steadily worsening across the coastal hills that surround the Los Angeles area. Early Thursday, the NOAA/NWS Storm Prediction Center placed a swath of the region under an “extremely critical” fire-weather risk, which is the most dire of SPC’s three fire-threat categories. The highest-end threat is expected to emerge in this area later Thursday and extend into Friday. More than 10 million people are in the extremely-critical risk area. A large area from the San Francisco Bay foothills into northern California is under an “extreme” risk for dangerous fire weather, the second-highest rating.
Yet another dangerous autumn for California
Fire weather typically peaks during the autumn in California’s Mediterranean climate. The state’s precipitation occurs mainly during the months from late autumn through spring. The landscape then dries out in the typically rain-free heat of summer, leaving it primed to burn at times when strong, dry autumn winds push through the area. The most dangerous setup is when east or northeast winds prevail, as the air warms and the relative humidity drops when these winds push downslope into the state’s extensive wildland-urban interface.
In keeping with recent years, California has just come off yet another scorching summer. State temperatures from July through September were the hottest for any July-to-Sept. period in 124 years of recordkeeping, according to the NOAA National Centers for Environmental Information.
Making matters worse, there has been very little rain so far this autumn. Paradise, CA, has received just 0.14” of total precipitation since October 1, which is a mere 3% of the long-term average of 4.49” for the period Oct. 1 – Nov. 7. Just to the south, Sacramento is having one of the ten driest starts to the wet season in its history, receiving a meager 0.04” on the only day of rain since October 1.
Between the summer heat and the lack of autumn rain, the amount of moisture held in soils and vegetation over parts of California is close to record-low levels.
The ingredients above are not unlike those in place last autumn, when the catastrophic Tubbs Fire tore across parts of the California North Bay region in October and the massive Thomas Fire ravaged vast areas northwest of Los Angeles in December.
The current weather pattern across North America doesn’t bode well for significant moisture across California anytime soon. A strong upper-level trough (an area of low pressure within a dip in the jet stream) is in place from central Canada into the Upper Midwest. Pulses of energy rippling along the jet stream will be reloading this trough over the next few days, keeping conditions cooler than average east of the Rockies while most of the West stays dry and unusually mild. It will likely be a week or more before California sees any chance of fire-easing rainfall.
For more on why California wildfires are so destructive in autumn, see the weather.com explainer.