Now, warning signs are again flashing red as another pronounced heat dome builds over the region. It is forecast to lead to more record high temperatures and bursts of fire-fanning winds.
The National Weather Service has posted red flag warnings for “critical” fire weather conditions for the East Bay and North Bay Hills near San Francisco from Saturday through Monday. Winds from the north will eventually come out of the east, blowing from land to sea, increasing temperatures and dropping humidity percentages into the teens and single digits.
The Weather Service office in San Francisco predicted the strongest winds between Sunday evening and Monday morning. Computer model trends are favoring stronger winds than were previously anticipated, forecasters wrote in a technical discussion.
Update: big heatwave and extremely dry airmass still on track. Unfortunately, models also trending a bit stronger and more widespread with offshore winds over NorCal this weekend. No doubt this will be a critical fire weather situation. #CAwx #CAfire https://t.co/7FdFp2M6an— Daniel Swain (@Weather_West) September 25, 2020
“To be clear this event is nowhere near the strength of the 2017 wine country, 2018 Camp or the 2019 Kincade fires,” the Weather Service wrote, speaking of some of the most deadly and destructive blazes in that region during the past few years. “However the setup is still critical.”
Red Flag Warnings are also in effect for a large part of Northern California, including the Sacramento Valley, parts of hard-hit Butte County, Lassen National Park, and parts of the Stanislaus National Forest, among other areas, for the Saturday night through Monday time period.
“The combination of wind, low humidity, and hot conditions will result in critical fire weather conditions,” warned the NWS office in Sacramento early Friday afternoon. “These conditions may impact ongoing wildfires. Extreme caution should be taken to prevent new fire starts.”
California utility Pacific Gas & Electric Co. said it may preemptively cut power to some areas depending on the fire weather conditions. The company’s electric transmission lines and other equipment have been identified as the cause of past fires, including the Camp Fire in 2018, which was California’s deadliest blaze.
Numerous fires, including the Creek Fire and the North Complex, are located in the region set to experience high temperatures and strong winds, which could lead to extreme fire behavior yet again.
High temperatures in the Sacramento Valley may exceed 100 degrees during the weekend into early next week, according to the Weather Service, and upper 90s and low 100s may be reached in parts of the San Francisco Bay region as well.
The Weather Service’s forecast office in Los Angeles is warning residents of a prolonged extreme heat event from Sunday through Friday, with high temperatures in the triple digits and “extreme fire behavior” with “large smoke plumes” accompanying preexisting and new blazes.
During the heat wave that hit California earlier this month, Los Angeles experienced an extraordinary temperature of 121 degrees, the highest recorded for L.A., Ventura, Santa Barbara and San Luis Obispo counties.
This next heat wave won’t be as pronounced, but it does not take much heat and dry winds to turn weather conditions decidedly in wildfire’s favor just after firefighters had made progress in containing some of the blazes.
“With no significant precipitation in sight, California remains dry and ripe for wildfires,” Cal Fire stated in a wildfire summary Friday.
The high pressure area responsible for the hot weather and renewed fire danger is likely to reach near-record intensity for that part of the country at this time of year, part of a trend toward strong areas of high pressure that effectively block other weather systems from moving into a region, earning the designation of a “blocking high.”
The weather pattern across the United States next week will feature the extreme heat associated with the high pressure area in the West, contrasted by a dip, or trough, in the jet stream bringing unusually cold air to the Midwest and East.
Thanks to climate change, heat waves are becoming more likely and intense. Some cases studies have shown that certain extreme heat events could not have occurred without human-caused global warming.
Californians have been suffering through weeks of hazardous air quality, which some researchers think have already killed more than have died through direct exposure to the fires, and any new fires or flare-ups in existing fire activity could prolong the air quality issues.
Scientific studies also show that by increasing air temperatures and drying out soils and vegetation, climate change increases the frequency and severity of days with extreme fire risk. This is true in the West, but also in other parts of the globe, according to a recent review of the scientific literature on this topic.
Land management practices along with the building of homes closer to forested areas that are susceptible to fires is another significant factor driving wildfire trends in the West, but it doesn’t account for the sharp increases in large fires seen in the past few decades.
One recent study, for example, found that climate change has doubled the days during the fall with extreme wildfire conditions in parts of California since the 1980s.