So far, no major wildfires have ignited during this event, though several small fires have broken out in Southern California.
According to the National Weather Service, the cause of this offshore wind event is a low-pressure area diving into the Great Basin. The air circulation around this feature is powering winds through mountain passes and up and over high terrain toward heavily populated areas in the state.
Typically, California’s biggest firestorms have occurred during periods of strong offshore winds such as this one. In an effort to prevent sparks from triggering any fires, Southern California Edison, the area’s biggest utility, is warning more than 100,000 customers that they may have power shut off as a preventive measure. Most of the customers are in L.A. and San Bernardino counties.
The 2020 wildfire season in California has been unrelenting, due to record warmth, a deepening drought, an abundance of lightning strikes and extreme offshore wind events.
Santa Ana winds resulted in major fires in Orange County in late October, forcing tens of thousands to evacuate on short notice. Now, though, vegetation is even drier because of the lack of significant rainfall, which makes the strong winds riskier.
The months of August, September and October each ranked as the state’s hottest since records began in 1895.
Without enough rain, high fire danger is continuing into November and December in Southern California, and the driest period is now coinciding with the windiest. Many lower-elevation locations, along with the mountains of Los Angeles and Ventura counties, have received less than a quarter-inch of rain since Oct. 1, which marks the start of the water year in the state.
For example, only 0.08 inches of rain has fallen in Camarillo in Ventura County. Typically that area should have received nearly two inches of rain since Oct. 1.
There are no significant rains in sight for Southern California, either. In fact, computer models project a large area of high pressure to build across the West in early-to-mid-December, diverting storm systems to the north and leaving the region milder and drier than average during the period. The Weather Service forecast office in L.A. is highlighting the potential for two additional Santa Ana wind events during the next week, including what could be a strong one during the middle of the first week of December.
The cool-season fire danger this year is reminiscent of December 2017 in Southern California and is consistent with a delayed arrival of autumn rains over the past several years, an effect that has been predicted to emerge in California because of human-caused climate change.
The Thomas Fire in Ventura and Santa Barbara counties was ignited by power lines during high winds on Dec. 4, 2017. It burned for more than a month, scorching 281,893 acres and destroying 1,063 structures.
Recent studies have shown that warming and drying fall seasons are amplifying the fire threat as the number of extreme fire-weather days increases and very dry conditions extend later into the year. This trend is the result, in part, of human-caused climate change and has also been seen in other parts of the world. One 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.
California is in the midst of its worst wildfire season on record, with about 4.2 million acres burned, more than double the acreage in the previous record-breaking year. At least 10,488 structures have been destroyed and 31 people killed. Five of the six largest fires on record in the state have occurred this season.
Diana Leonard contributed to this report.