An unusually warm autumn heat wave is continuing to push temperatures up across California, heightening fire risks across the state and prompting power shutoffs in the north and additional wildfire evacuations in the south.
Heat advisories, many warning of temperatures in the triple digits this week, have been issued throughout the state, from San Diego through Redding, with most areas expecting highs at least 10 to 20 degrees above average for this time of year, according to the National Weather Service.
While fire season in California typically stretches through October or November, this kind of heat is abnormal for the season, helping dry out landscapes and drop humidity levels, which officials expect to more easily and quickly foster wildfire growth.
As early as Monday morning, the effects of the heat wave were evident, with Pacific Gas & Electric following through on warnings that it would cut power to residents facing dangerous fire weather, particularly “high winds and dry conditions.”
Paul Doherty, a spokesperson for PG&E, said that power had been shut as of Monday morning for about 9,500 customers in Butte, Shasta, and portions of Glenn, Colusa and Tehama counties, with more shutoffs possible across Northern California, a decision that would be “based on real-time weather conditions.”
A total of 12,371 customers in 11 counties, including Alameda, Contra Costa, Humboldt, Sonoma and Trinity counties, and two tribal areas could be affected by the outages, which are possible through Tuesday evening, Doherty said. The shutoffs are meant to minimize fires igniting during high-risk weather, especially since several deadly and destructive blazes in recent years were started by utility equipment.
As temperatures began to climb in Southern California Sunday, authorities ordered additional evacuations and warnings because of flareups on the Line fire in San Bernardino County — which has been burning for almost a month. The 43,000-acre fire is still considered 80% contained, but increased heat in the area expanded the fire this weekend, which exceeded firefighters’ expectations, the California Department of Forestry and Fire wrote in a Monday update.
“The dry vegetation, steep slopes and wind aligned yesterday to create conditions for the rapid fire spread,” Cal Fire officials said.
Nearby, the Bridge fire in the San Gabriel Mountains is 97% contained after burning through almost 55,000 acres in both San Bernardino and Los Angeles counties, including more than 80 buildings that were destroyed, according to Cal Fire. The Airport fire, in Orange and Riverside counties, was 95% contained, after destroying 160 structures and scorching about 23,500 acres.
Across Southern California, the National Weather Service is warning of “dangerously hot conditions” Tuesday through Thursday, with highs reaching up to 105 degrees in several areas, including the San Fernando Valley, Santa Clarita Valley, Antelope Valley foothills and Interstate 5 corridor, the area’s excessive heat watch said.
These conditions, especially in the mountains, could help spark “plume-dominated fires,” characterized by tall plumes of smoke that become exceptionally hot, which can cause fires to erratically grow, said Bryan Lewis, a National Weather Service meteorologist in Oxnard.
“California looks much warmer than average for the foreseeable future, with little or no prospect of rain anywhere,” Daniel Swain, a UCLA climatologist, said in a recent online briefing. The National Weather Service’s Climate Prediction Center expects above-average temperatures to persist through at least mid-October across California, with much of the West forecast to remain warm all month.
This wave of summer-like heat is stretching across the Southwest, with Phoenix already enduring almost a week of record high daily temperatures, hitting 113 degrees Sunday. Some daily temperature records were also set in Las Vegas and the surrounding area this past weekend. Death Valley is expected to top out at 115 degrees over the next few days.
“Another unseasonably warm day is in store as temperatures remain 10-15 degrees above normal,” the National Weather Service office in Las Vegas tweeted on Monday. “Stay cool and hydrated out there.”
Swain, on X, called it an “anomalously warm and dry pattern,” which will likely bring rare, late-season heat to the interior that could set temperature records in parts of California, continue to drive dangerous fires and delay the state’s rainy season.
“The warm and dry autumn that has already started to unfold and [is] likely to continue in the coming weeks will set the stage for an unusually late fire season across the interior West,” he said.
Through Tuesday, parts of Del Norte and Humboldt counties in northwest California are under a red flag warning, signaling severe fire weather, with high winds driving the fire concern.
Gusty offshore winds over the next few days could be a concern across much of the California coast this week, especially given the higher temperatures, the National Weather Service warned.
Beyond fire hazards, meteorologists are warning of health risks that come with excessive heat. The National Weather Service in the Bay Area is warning of temperatures that could cause heat illnesses — up to to 104 degrees in the North Bay and East Bay mountains and valleys from Monday through Wednesday.
“Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors,” the heat advisory said. “Children and pets should never be left unattended in vehicles under any circumstances.”
Much of the Central Valley is also expected to see temperatures reach or surpass 100 degrees this week, with some areas of the San Joaquin Valley and Sierra Nevada foothills expected to near monthly record highs.