Much of Southern California from the mountains of Ventura County to the valleys of San Diego County is expected to be under a red flag warning for wildfire Thanksgiving week because of gusting Santa Ana winds, single-digit humidity and a warming trend, weather officials.
Relative humidity could plummet down to about 3% in parts of Riverside, San Bernardino and San Diego counties as winds gust as high as 80 mph in remote mountain and forest areas.
Also under a warning will be parts of Orange County, including the Cleveland National Forest, said James Brotherton, a meteorologist for the National Weather Service in San Diego.
Wind advisories call for gusts of up to 50 mph in the San Fernando Valley and Santa Monica mountains. In L.A. County the red flag warning is for the mountains and the Santa Clarita Valley. The advisory will remain in effect until 6 p.m. Wednesday.
But the greatest danger will probably to be in places like San Diego County, which have seen drier temperatures than L.A., said Brotherton, whose area includes the Inland Empire, and Orange and San Diego counties.
"It's not quite as severe in the L.A. region," he said.
"We're drier and windier and things are coming together to hit us more strongly down here."
Red flag warnings often trigger fire departments to send resources, including firefighters, to more vulnerable areas. L.A. County Fire Department Capt. Brian Jordan said five engines were sent Sunday to the Malibu area, and more than 50 firefighters to Malibu, Agoura and the Santa Clarita Valley. The added staffing is expected to continue, he said.
"There's a lot of firefighters receiving phone calls to come in to work," Jordan said.
He said there were gusts of 71 mph in the Malibu Hills, and winds were so strong that a county fire helicopter crew chose not to land in the wind-swept Malibu area Sunday morning.
Red flag warnings are also a reminder to people to be careful about not igniting a fire as they hike or travel in certain areas. By some estimates, about 90% of brush fires and wildfires are caused by humans. Brotherton said there were no lightning storms in the forecast, so if there is a large fire, it's almost certainly going to be caused by someone, either willfully or accidentally.
Southern California is expecting to see temperatures creep up into the upper 80s in parts through Wednesday, with a dip in temperatures beginning after Thanksgiving day. But that day will still be warm, in the mid- to lower-80s.
"It's kind of like happy Thanksgiving and pass the sun tan lotion," said David Sweet, a meteorologist for the National Weather Service in Oxnard.
By Friday, temperatures in L.A. should decline further to the mid- to high-70s, continuing a cooling trend into next weekend, Sweet said.
That will also happen in the Inland Empire and San Diego County.
The one thing Southern California needs is rain – and there's no rain forecast through next weekend. The National Oceanic and Atmospheric Administration said there's still about a 50% chance of an El Niño developing in the equatorial Pacific.
But even if that happens, the ocean pattern that arises out of the warming of sea surfaces isn't a reliable harbinger of above-normal rain unless the El Niño is strong. If it develops, scientists said this year's El Niño would almost certainly be weak.
"With weak El Niños, there is no specific signal as to a dry year versus a wet year," Sweet said.