Wildfires in California are spreading rapidly with extreme fire behavior — an ominous sign for the autumn months when the state typically sees its most destructive fires.
By Wednesday morning, it had reached more than 50,000 acres, with a long list of communities under evacuation orders and warnings.
The monstrous Dixie Fire has covered even more ground in the last few days, adding over 66,000 acres since Monday for a total of 635,728 acres burned. The McFarland and Monument fires now both exceed 100,000 acres and can be considered “megafires.”
Even seasoned professionals in the firefighting community are shocked at what has unfolded so far this summer and the speed with which fires are moving.
“We know this fire has done things that nobody could have predicted, but that’s how firefighting has been in the state this year,” Jeff Marsolais, Eldorado National Forest supervisor, said during a Tuesday community meeting for the Caldor Fire. “I’ve spent four weeks in the North State, and every time a fire broke [out], it outpaced our models 2 to 1.”
Given the explosive conditions, Marsolais issued an emergency closure for the entire Eldorado National Forest through Sept. 30 “in response to the extreme fire behavior demonstrated by the Caldor Fire, and risks to public and firefighter safety.”
Red-flag warnings for gusts and high fire danger blanket much of Northern California through Thursday. Although the winds aren’t remarkable, they threaten dangerous runs by the many large fires burning in the region and the rapid spread of any new ignitions.
The volatile situation is a reflection of just how flammable the state has become: It entered the summer in deep drought and then experienced its hottest June and hottest July on record.
Given high levels of flammability, it doesn’t require much wind to set landscapes ablaze.
“As has been exemplified by the relentless Dixie fire, today’s eruption of the Caldor fire, and the other ongoing large fires today and in recent weeks, much of the region away from the coast is primed to burn,” the National Weather Service’s San Francisco office wrote in a forecast discussion. Weather elements such as wind and dry air “dramatically exacerbate the already existing risk,” the office said.
As the region enters a #RedFlagWarning, live fuel moistures are becoming drier than ever. Currently, 51% in Los Gatos. This is the driest FMC recorded at this site. Please be careful out there! #CAfire #CAwx #FireDanger pic.twitter.com/1LN2IkHOd9— SJSU FireWeatherLab (@FireWeatherLab) August 18, 2021
A trough, or dip in the jet stream, digging into the Intermountain West and combined with a ridge of high pressure off the coast has set up a pressure gradient that is driving winds through California on Wednesday. North-to-northeast winds gusting between 35 and 50 mph arrived Tuesday evening and were expected to peak Wednesday morning and continue into Tuesday in some areas, such as Sacramento Valley. The winds are also expected to disperse smoke across the state.
Dry northerly winds over northern California will transport smoky/hazy conditions over the Bay Area through midweek. While some smoke may mix down to the surface, @AirDistrict forecast air quality to remain at moderate levels. #CAwx #BayAreaWX pic.twitter.com/FewUuPNiwR— NWS Bay Area (@NWSBayArea) August 18, 2021
To avoid sparking new blazes, Pacific Gas and Electric began to cut power Tuesday evening to 51,000 customers in parts of 18 counties. It planned to restore service Wednesday as winds weaken.
“The safety shutoff is due to a combination of dry offshore winds, extreme to exceptional drought conditions and extremely dry vegetation,” the company wrote in a news release.
This week’s shut-offs are smaller in scope than some that occurred in previous years. For example, PG&E de-energized 345,470 customers between Oct. 25 and 28, 2020 — its largest “Public Safety Power Shutoff” last year for a much stronger and more widespread wind event than is occurring this week.
However, California will almost certainly see stronger winds in the coming months. Dangerous fire behavior this summer does not bode well for autumn, with the offshore wind season set to ramp up in September. Given warmer and drier-than-normal weather expected into October and November, conditions could be even more combustible when the state faces its fiercest winds.
Diana Leonard is a science writer covering natural hazards in California.