Santa Ana winds will bring extremely dangerous fire conditions and power shut-offs this week

Weather forecasters are urging extreme caution as strong Santa Ana winds blowing through Southern California will bring very dangerous fire conditions and possible power shut-offs this week.

A red flag warning for this “particularly dangerous situation� is in effect through Saturday for the mountains of Los Angeles and Ventura counties as well as the Santa Clarita Valley, the National Weather Service said.

Winds will peak Thursday and are expected to reach up to 40 mph, with 70-mph gusts. Humidity levels will be between 8% and 15% on Thursday and will decrease Friday and through the weekend to between 5% and 10%.

The combination of the extended offshore flow and dry air could lead to devastating fires.

Weather service officials said the high winds will last longer than normal, waning in the weekend. But it’s possible the red flag warning will be extended through Tuesday.

“We are urging the public to be extremely cautious with anything that can start a fire,� weather service officials said in a forecast discussion. “Some ignition sources are obvious [such as campfires, welding equipment, cigarettes, fireworks] but others are less so [such as lawn trimmers, dragging trailer chains, firearms].�

Los Angeles County firefighters have beefed up their staffing around the clock in preparation.

“We got lucky last weekend, and we’re hoping that same luck keeps running through this one,� said fire inspector Henry Narvaez.

Strike teams, or small groups of firefighters, have been deployed on 24-hour shifts to stations in Malibu, Santa Clarita and La Cañada Flintridge, and pilots are on standby Thursday through Saturday, Narvaez said.

On Wednesday, Southern California Edison began shutting off power to customers in wind-prone areas, starting with about 900 customers in Los Angeles and Ventura counties, utility officials said.

Up to 270,000 additional Edison customers, including people in San Bernardino, Orange and Riverside counties, may lose power Thursday or Friday and will have to wait for utility crews to inspect the grid before it can be restored, a process that can take a day or more in some cases.

The upcoming winds will hit the same parts of the Southland that were buffeted by 70- and 80-mph gusts in October, when a pair of fires moved into suburban Orange County, but this time the winds should be less severe, said National Weather Service meteorologist Alex Tardy.

“Nevertheless, this is a strong wind event for wind-prone areas and moderate for many areas,� Tardy said. “If a fire were to start … there would be some problems with containment.�

But given the time of year and duration of the upcoming system, forecasters say the Santa Ana winds could hang around for up to 10 days, extending into next weekend. This would be a weather pattern similar to the one seen in December 2017, when several fires broke out across the region in 72 hours, including the massive Thomas fire.

“It’s common to see Santa Ana winds in December, but we’re not usually critically dry,� Tardy said.

According to the National Oceanic and Atmospheric Administration, a La Niña climate pattern is ongoing, gathering strength in the tropical Pacific Ocean this year.

Statistically, a La Niña favors warmer, drier conditions across the southern tier of the U.S. and cooler, wetter conditions in the north.

The lack of summer monsoon rain this year resulted in extreme to exceptional drought in the Southwest. According to the U.S. Drought Monitor, moderate to severe drought expanded in California’s San Joaquin Valley, and abnormal dryness expanded in Southern California, including Los Angeles County. Parts of Southern California have experienced a seven-month dry streak.

This season in Los Angeles, only 0.11 of an inch of rain has fallen. In an average year by the end of November, the city has received close to 1.7 inches, making rainfall this year about 6% of normal.

Times staff writer Paul Duginski contributed to this report.