The fire danger will rise thanks to northeasterly winds and plummeting humidity beginning late Wednesday and extending until early Friday. Wednesday evening into Thursday afternoon looks to be the most dangerous time for potentially rapid fire spread should ignition occur.
The area at greatest risk stretches from the northern Coast Range and foothills through the Sacramento and San Joaquin valleys, as well as the northern Sierra Nevada.
North and northeasterly winds will gust 30 to 40 mph in the foothills, and closer to 50 mph in the mountains. The “downsloping” effect means any air swept downhill will both dry out and accelerate, sapping ground vegetation of moisture. Relative humidities could fall as low as 10 to 15 percent. Napa and Sonoma counties are areas of particular concern.
Threat expands south by Thursday
Those same tinderbox conditions will overspread central and southern California by Thursday morning. A fire weather watch includes Los Angeles and reaches down to the Mexico border. Their dangerous weather will be even more intense, with high temperatures in the mid- to upper 90s, humidity as low as 2 percent and stronger winds reaching up to 60 mph in the mountains.
The forecast is for “widespread critical conditions to Los Angeles and Ventura Counties,” the National Weather Service in Los Angeles wrote in its morning forecast discussion. The agency went further on an ominous note, stating, “This has all the makings for a dangerous fire weather scenario, similar to worse than the recent October 10-11 event that produced the Saddleridge Fire.” The Saddleridge Fire, which has since torched 8,800 acres, was at 92 percent containment Tuesday.
With this upcoming streak of fire weather, the danger will not wane at night. Instead, sundowner winds — caused by the cooling and downhill surge of air adjacent to the mountains — will kick in after dark. And with little overnight recovery in humidity, this has the makings of a 48-to-72-hour period of extreme fire danger.
Conditions will improve into the weekend for Northern and central California, and by early next week to the south.
Planned outages are a new reality
Ahead of the dangerous forecast, utility provider PG&E has advised 209,000 customers of a potential “public safety power shut-off” planned in Northern California, depending on how the forecast evolves. Among those affected are 9,197 “medical baseline” customers who depend on electricity for various health reasons. Each customer has been notified of the possible shut-off; electric-dependent customers with medical issues who have not responded to PG&E’s notification will be visited by a company employee.
“If you rely on electric or battery-dependent medical technologies such as assistive technology, breathing machines, a power wheelchair or scooter & home oxygen or dialysis, it is critical that you have a plan in place for an extended power outage,” tweeted the company Monday night.
A number of “community resource centers” will open Wednesday “to provide restrooms, bottled water, electronic-device charging and air-conditioned seating” for those who experience a severing of electric service.
The “public safety precautionary shut-offs” are a new implementation by PG&E, after the sparking of the Camp Fire in 2018. That fire killed 86 people, reducing the town of Paradise to ashes. PG&E reached an $11 billion settlement that covers Northern California fires from 2017 and the 2018 Camp Fire. This could be the second precautionary shut-off in California this month. Between Oct. 9 and 12, power was cut to more than 738,000 customers in 30 California counties because of the wildfire threat.
One of the most robust conclusions of climate change research is that wildfires are becoming increasingly frequent and severe in large parts of the American West as the climate warms, particularly in California. This is occurring as summers become hotter and drier and precipitation becomes more variable in the winter, with lurches from drought to flood and back again becoming the norm.
In an indication that an uptick in large wildfires is already occurring in California, 15 of the top 20 largest wildfires in state history have all occurred since 2000.
Andrew Freedman contributed to this report.