In addition, the North Bay Mountains, East Bay Hills, Santa Cruz Mountains, San Mateo coast and other areas are under a red flag warning from Wednesday night through Friday morning for strong winds and low humidities as winds blow from land to sea at up to 40 mph.
Areas further to the north, closer to the Oregon border, are also under red flag warnings at different times through Friday.
“Cal Fire has increased staffing and is on high alert,” the state firefighting agency said in a situation report Tuesday. “Officials are urging the public to ensure they are prepared for wildfires, as well as take all precautions outdoors to prevent sparking a wildfire.” About 7,000 firefighters are on duty with 22 wildfires active around the state, including 12 large blazes.
The next push of winds, which will be related to a cold air mass moving to the east of the state beginning Wednesday night, may be stronger than the first that affected northern California earlier this week, with northeasterly winds gusting to 40 mph, andstronger gusts at night and in the early mornings.
Similar northerly wind events have been associated with some of the rapidly spreading fires that have already scarred the landscape from California wine country to the high-elevation forests of the Sierras. Computer model projections show additional northerly wind events that may occur this weekend into early next week, as well, as somewhat cooler air funnels into the state, but precipitation prospects stay near zero.
“Forecast confidence is increasing for a potential third offshore wind event later in the weekend into early next week as a cold trough dives in the Great Basin,” the Weather Service forecast office in San Francisco wrote in a technical discussion Tuesday morning. “This type of pattern would likely result in stronger northerly winds than the two preceding events this week, with winds likely peaking on Sunday night.”
Daniel Berlant, Cal Fire assistant deputy director, said the ongoing Red Flag warnings and weekend wind threat are especially concerning because as the state gets deeper into the fall, its trees and shrubs are at their driest. Late season wind events, Berlant said, are particularly hazardous.
“There is the potential that we could have another destructive few weeks” or even months, Berlant said in an interview, depending on the timing of winter rains. “We’re definitely at an all hands on deck situation,” he said.
In response to the fire weather concerns and strong winds in the forecast, Pacific Gas and Electric is conducting preemptive power shut-offs to reduce the odds that its infrastructure could provide the spark to another deadly wildfire. The utility has been blamed for the state’s deadliest fire, known as the Camp Fire, that devastated Paradise, Calif., in 2018.
Recently, PG&E has been conducting more targeted power cuts, rather than larger-scale reductions in electricity transmission that took place earlier in this year’s wildfire season.
Since the start of the year, more than 4.1 million acres have burned in California, with 31 fatalities and more than 9,200 destroyed structures, according to Cal Fire. Five of the top six largest fires in state history have occurred in 2020, including the largest, the August Complex. That blaze has become the state’s first “gigafire,” having burned more than 1 million acres so far.
Meanwhile, in the Rockies, the upcoming weather pattern shift toward colder-than-average temperatures and potential snowfall will eventually act to lessen the fire threat in Colorado, where the largest fire in state history is burning near Fort Collins.
Another fire in Boulder County has destroyed 26 homes and prompted evacuations, and firefighters would welcome cold temperatures and snow after battling warmer-than-average weather and strong winds over the weekend.
However, before colder air and potential snowfall arrives this weekend, there’s a potentially perilous period of high winds and low humidity that will affect both the CalWood Fire in Boulder County and the Cameron Peak Fire west of Fort Collins.
Winds moving from higher elevations to lower altitudes, known as down sloping winds, could reach 40 to 50 mph at times between Wednesday and Friday, the Weather Service said. Red flag warnings are in effect for mountain valleys Wednesday afternoon and evening, with the strongest gusts shifting to the Front Range foothills this afternoon and overnight. The Front Range foothills are also under a red flag warning for that reason.
The wind patterns may shift at times, which if the fires increase in intensity, could complicate firefighting efforts.
The large, destructive wildfires of 2020 have clear connections to human-caused global warming, studies show. An analysis of the 2020 fire season to be published in Global Change Biology, for example, ties California’s record fire season to hotter and drier weather that has taken moisture out of vegetation and soils with greater efficiency.
“In California, an eight-fold increase in forested burned area over the last half-century is tightly linked to increased atmospheric aridity,” the study says. “With each passing fire season, we are experiencing what dozens of studies have projected and warned of, for decades, as a consequence of a warming climate: increased area burned throughout the 21st century.”