Thanksgiving weather forecast: biting cold

Wear a sweater or hang around the roasting turkey. It’s going to be a nippy Thanksgiving weekend.

Courtesy of the Gulf of Alaska, the jet stream has been swooping down and bringing storms and cold air to the Pacific Northwest, down through Northern California to the Southland. It’s been cold, and it’s expected to stay that way through the holiday weekend. A strong, cold Santa Ana wind could blow into Thursday evening, with gusts of more than 60 mph along mountain passes and ridges. There’s also a slight chance of rain Saturday or Sunday.

The National Weather Service warned of freezing temperatures — as low as 16 degrees — into Thursday morning in many of Los Angeles’ mountain and desert areas, including Mt. Wilson and large parts of the Antelope Valley. Some valley locations could hit the freezing point.

The weather service warned residents to protect sensitive outdoor plants and crops, and to keep pets and animals indoors or in a barn.

Jay Van Rein, a spokesman for the California Department of Food and Agriculture, said that based on the forecast, there were concerns about citrus crops, particularly in the Central Valley from Fresno County to Kern County. Three years ago, record cold temperatures destroyed most of the oranges still hanging on trees.

But Vanrein said this cold snap was not expected to be nearly as severe.

“There are freezing temperatures forecast, but for a much smaller range of time and a smaller range of geography,” he said. “There may be some losses, but if this follows the forecast, most of the growers should be able to take measures to protect their crops and minimize their losses.”

For downtown Los Angeles, Monday’s high temperature was 9 degrees below average. On Tuesday, when the temperature dipped to 61 degrees, it was 6 degrees below average, said Bill Patzert, a climatologist for the Jet Propulsion Laboratory in La Cañada Flintridge. Low temperatures in the Los Angeles Basin have hovered around 40.

“It’s going to be cold and windy pretty much. That’s the story of Thanksgiving,” said Bonnie Bartling, a weather specialist for the National Weather Service in Oxnard. “We’re having a cold Santa Ana event.”

Though it’s been cooler than normal recently, the Los Angeles area hasn’t exactly had many normal days of late, weather experts say. Downtown Los Angeles recorded temperatures in the mid- to high 90s early in the month, before temperatures quickly dipped into the 70s. Then the temperatures toggled between the 60s and the 70s before descending back into the 60s.

Daytime temperatures at Mt. Wilson are expected to hover in the mid-40s, and desert communities like Lancaster are expected to see temperatures in the high 40s, with nighttime temperatures expected to go down below 20 degrees, Bartling said. By Sunday, the snow level could drop to about 4,000 feet, according to the National Weather Service.

The valleys, and much of the rest of Los Angeles, including the beach areas, are expected to remain in the 60s through the weekend.

Patzert said that the cooler temperatures are consistent with cooling temperatures in the equatorial Pacific strengthening into a relatively vigorous La Niña. Unlike El Niños, which often create warmer and wetter than average conditions in Southern California, La Niñas are more reliable omens of dry and cold temperatures, Patzert said.

Despite light rains, Los Angeles has recorded lower than normal rainfall, with only about 1.35 inches of rain falling in downtown since July 1.

Since 1949, there have been 22 La Niñas, and during 18 of them the region saw below normal rainfall, he said. But an “amped up” jet stream from up north could increase the chances of rain.

Still, the only sure thing Thanksgiving weekend, Patzert and Bartling said, seems to be cold.

“This is the kind of thing you usually get in December and January, where you really get a cold snap,” Patzert said.

hector.becerra@latimes.com