SAN DIEGO (AP) -- Zookeepers turned up the heat for chimpanzees and strawberry growers covered their crops as Californians braced Friday for three days of freezing temperatures.
The cold snap is expected to last through the weekend.
Morning temperatures fell into the 20s and 30s in many areas, and much lower in the mountains. A low of 12 degrees was recorded in the Big Bear mountain resort east of Los Angeles.
In Sonoma County, homeless shelters started handing out extra warm clothes to protect people from below-freezing overnight temperatures.
Central Valley citrus growers watched as temperatures dipped into the 20s Friday. Napa, in wine country, and Sacramento, farther north, both recorded 27.
High temperatures in the Central Valley over the weekend were forecast for 50 degrees, according to the National Weather Service.
In the south, forecasters warned that a low pressure trough sinking over San Diego County and parts of neighboring Orange County could keep nightly temperatures below the freezing point in coastal areas, the low deserts and inland valleys, threatening orange and avocado orchards and other sensitive plants. The coldest nights were expected to hit Friday and Saturday.
Farmers prepared to pull out giant fans to circulate the air and keep it from settling on their citrus trees, said Eric Larson of the San Diego County Farm Bureau.
"These guys are going to be up all night watching thermometers," Larson said.
Workers at SeaWorld in San Diego planned to crank up the heat for their macaws, toucans and parrots. San Diego zookeepers were also heating rooms for chimpanzees, apes and other tropical animals.
"They'll probably be huddling together and not be in areas where people will be able to see them," zoo spokeswoman Christina Simmons said.
Authorities on Friday reopened a 40-mile stretch of a major highway north of Los Angeles -- some 17 hours after snow shut the route and forced hundreds of truckers to spend the cold night in their rigs.
The California Highway Patrol shut the Grapevine segment of Interstate 5 on Thursday afternoon. Officers began escorting traffic southbound early Friday and then opened northbound lanes about an hour later.
The shutdown severed a key link between the Central Valley and Los Angeles.
"There must have been 1,000 Mack trucks lined up," said traveler Heidi Blood, 40.
Blood and her three youngsters had been visiting Orange County and set out at 4:30 a.m. for their home in Kentfield when they found the road closed.
"I usually watch the news but I went to a spin class instead. I learned my lesson," Blood said.
Blood had to give an insulin shot in the car to her 13-year-old blind, diabetic dog, Barney.
To pass the time, the family watched movies and read on their iPads, turning on the car every 30 minutes to use the heater.
"We're watching 'Nannie McPhee' in the car right now," Blood said. "I only have enough juice for another three hours."
The highway through Tejon Pass rises to 4,100 feet in the Tehachapi Mountains and frequently is shut down in winter by blowing snow and treacherous black ice on the roadway.
Associated Press writer Jason Dearen in San Francisco and Robert Jablon in Los Angeles contributed to this report.
Copyright 2013 The Associated Press.