Other fires have also developed across the heavily populated region, including one threatening homes in Yorba Linda.
The National Weather Service office in Los Angeles warned of winds gusting as high as 90 mph in higher elevations, calling it “a particularly dangerous situation.”
“That area has a lot of grasses and they burn fast,” said Alex Tardy, warning coordination meteorologist for the Weather Service’s San Diego office, about the Silverado Fire. “It’s just moving very quickly into the urban areas.”
Smoke from the fire is moving horizontally or “laying flat” — a sign of a dangerous fire that is being pushed by very strong winds. Winds are gusting to 40 mph in the area, and Fremont Canyon, a typically windy zone north of the fire, recorded a peak gust of 88 mph Monday.
Southern California had some light rain and clouds Sunday, but the weather quickly shifted and a rapid drying occurred with the arrival of Santa Ana winds early this morning.
Meanwhile, powerful northerly winds were blowing in Northern California. Winds in the Sierra Nevada Mountains have been the strongest in the state, with a gust to 140 mph recorded at Kirkwood Mountain, where sustained winds were clocked above 100 mph.
These land-to-sea winds, locally known in northern parts of the state as “El Diablo,” and “Santa Ana” winds in the south have brought in extremely dry air, causing the relative humidity to plunge into the single digits.
With the air so dry, winds so strong and vegetation, or fuels, already at record dry levels for this time of year, the state is poised to burn. The focus for officials has been on depriving lands of an ignition source.
Red flag warnings are up throughout the Golden State, from San Francisco to Sacramento all the way to the northern border with Oregon, and extending south into the Los Angeles and San Diego metropolitan areas as well. In some locations, these warnings last through Wednesday.
As of Monday afternoon, fires flaring up in Southern California were the main focus of concern.
Any blaze that occurs Monday will probably exhibit extreme fire behavior, including rapid rate of spread. The strong winds even halted flights for at least one California airport, with Ontario Airport shutting down for a time because of severe crosswinds.
In addition to networks of fire-spotting cameras, firefighters are using heat-sensing equipment aboard a National Oceanic and Atmospheric Administration (NOAA) satellite to quickly find any developing blazes and direct firefighters to them.
The Weather Service forecast office in Los Angeles said the Santa Ana winds there are the strongest the region has seen this year and have the potential to contribute to a conflagration through Tuesday. So far, winds have gusted as high as 96 mph in the San Gabriel Mountains, the Weather Service reported.
Forecasters called this severe weather event “the most dangerous fire weather conditions we have seen since October 2019.”
“A particularly dangerous situation is expected for the Los Angeles County mountains from 2 pm to 11 pm [Monday] due to the combination of damaging wind gusts of 60 to 75 mph, single digit humidities, and critically dry fuels,” forecasters wrote in a technical discussion on a Weather Service website. “New fire ignitions in Los Angeles and Ventura counties will have the potential for very rapid fire growth, extreme fire behavior, and long range spotting, resulting in a significant threat to life and property.”
The Storm Prediction Center in Norman, Okla., which issues fire risk outlooks for the United States, placed Southern California in its highest threat category of “extremely critical” fire danger because of high winds, low humidity and record dry vegetation.
In preparation for the winds and fire risk, the utility company Pacific Gas & Electric preemptively cut power to hundreds of thousands of Californians. On Monday at about 5:45 p.m. Eastern time, about 456,000 customers were without power across the state, according to Poweroutage.us.
During the past few years, the company’s infrastructure, including transmission lines, have been blamed for some of the state’s deadliest and most destructive blazes, including some of the wine country fires and the 2018 Camp Fire, which nearly destroyed the town of Paradise, Calif., and killed dozens.
On Friday, Berkeley took an extraordinary step in recommending that residents who live in the fire-prone hills of the city consider evacuating ahead of Sunday’s predicted winds — and even noted hotels that are offering discounts in the better-protected urban core. The Weather Service has expressed concern about upcoming conditions in the East Bay hills, referencing the 1923 fire in Berkeley and the 1991 Tunnel Fire in the Oakland Hills.
Ties to jet stream buckle that brought an Arctic outbreak
The high wind event is the result of a push of a record-setting Arctic air mass into the Rockies and Great Basin along with strong winds at the upper levels of the atmosphere. When low-pressure areas riding along the jet stream land in Colorado, high-pressure zones build in quickly to their north and west over northern Nevada and Utah, a region known as the Great Basin. The difference in pressure over this relatively short distance starts generating these winds.
The winds are then drawn westward toward California, where air-pressure readings are lower (air flows from high to low pressure), and often, they gain speed passing through channels in the high terrain. As the air moves down mountain slopes, it dries out further.
This particular high wind event is shaping up to be what many meteorologists had feared the most for the Golden State this year: an extremely dry, land-to-sea (also known as offshore) wind event just when the region is at its most parched.
Climate change increases the chances for fall wind, dry conditions to overlap
California is in the midst of its worst wildfire season on record, with more than 4.1 million acres burned, which is more than double the acreage burned in the previous record-breaking year. In addition, at least 9,200 structures have been destroyed and 31 people killed. A staggering five of the top six largest fires on record in the state have occurred this season, including the largest, the August Complex.
That fire is also the state’s first “gigafire” on record, having burned more than 1 million acres.
To see a longer-term perspective: 17 of the top 20 largest blazes in the state have taken place since 2000.
Scientific studies 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 world, according to a recent review of the scientific literature.
California has seen its fire season lengthen, which causes the driest time of year to increasingly overlap with the typical season for the state’s strongest fall offshore wind events.
This year, the state saw its hottest August on record, with sizzling temperature records. Then an even more severe heat wave struck in early September, leading to a firestorm of historic proportions. Fuels that have not burned are at or near record-dry levels.
Land management practices, along with the building of homes closer to forested areas susceptible to fires, are other significant factors driving wildfire trends in the West, but they don’t explain the major uptick in large fires in recent years.
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.
Diana Leonard contributed to this report.