Santa Ana winds howl from Los Angeles County to San Diego, escalating risk of fire

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It’s almost December, typically a time of regular rainstorms and mountain snows in California. But instead millions from the Los Angeles area to San Diego are experiencing a dangerous Santa Ana wind event that is raising fire risks to “critical” levels, the second-highest threat category.

Red Flag warnings along with warnings and advisories for high winds are in effect for downtown L.A., and inland areas of San Diego counties, with wind gusts so far exceeding 80 mph in some mountain areas. Santa Ana winds are expected to continue to whip across the region through Saturday, sending air moving from inland areas to the sea. As the air descends from the mountains it compresses and dries out, leading to extremely low relative humidity levels, in the single digits in some areas.

So far, no major wildfires have ignited during this event, though several small fires have broken out in Southern California.

According to the 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 lose power 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.

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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, due to 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 2 inches of rain by now 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 to occur 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 last several years, an effect that has been predicted to emerge in California due to human-caused climate change.

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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 top six largest fires on record in the state have occurred this season.

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