Gregory Bull / AP
Esteban Gasca of Chula Vista, Calif., takes a picture after forming the Spanish word, "amo," or "love," with rocks on a beach as clouds from a nearby cold front make their way inland on Friday in San Diego. Few people frequented the city's famous beaches as Southern California braces for a cold snap expected to drop temperatures to a six-year low.
Updated at 4:30 p.m. ET: Californians are bundling up with sweaters and gloves and stocking up on firewood as they brace for several nights of freezing temperatures.
The National Weather Service is forecasting morning frost on San Diego beaches. Big Sur, on the central coast, prepared for daytime highs almost 20 degrees below Boston's. Even the snowbird haven of Palm Springs faced the possibility of freezing temperatures at night.
In addition, San Diego zookeepers turned up the heat for chimpanzees and some farmers broke out wind machines and took other steps to protect crops from freezing.
Freeze warnings were in effect in San Diego County valleys and deserts Saturday morning with lows in the 20s and 30s, the weather service said.
In Sonoma County, homeless shelters started handing out extra warm clothes on Friday to protect people from freezing overnight temperatures.
Arizona faces its coldest night time temperature in years, threatening crops. Meanwhile, the weather is spring-like in parts of the East Coast. NBC's Kristen Dahlgren reports.
Morning temps 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.
By midday Saturday, the temperature had warmed to the mid-50s – balmy for most everywhere else in the country but frigid in Southern California.
In an official weather advisory on Saturday, the National Weather Service wrote: "The bad news for those people who don't like cold temperatures is that any moderation in these frigid conditions is forecast to be slow heading into next week, with below-normal readings continuing."
It was, the Weather Service noted, a contradiction: The West Coast, usually mild-weathered, was uncharacteristically cool. Parts of the East Coast, by contrast, boasted spring temperatures. The Appalachians could see highs in the 60s and 70s -- at least 20 degrees above average.
'Crazy busy' at firewood store
Some customers drove more than an hour to buy firewood.
"It's crazy busy here," said Renea Teasdale, office manager at The Woodshed in Orange, south of Los Angeles.
Still, it was business as usual as much of the state contended with temperatures in the high 40s and low 50s.
"It's still sunny Southern California, and I'm going to work on my legs all year long," said Linda Zweig, a spokeswoman for the Del Mar Fairgrounds, which is hosting a 5-kilometer (about 3-mile) run north of San Diego on Sunday. The lifelong San Diego-area resident is prone to wearing two sweatshirts when the temperature drops but refuses to give up on shorts.
In the San Joaquin Valley, the heart of California's citrus production, growers prepared for another round of freezing temperatures late Friday after seeing little crop damage Thursday night.
They run wind machines and water to protect their fruit, which can raise the temperature in a grove by up to 4 degrees, said Paul Story, director of grower service at California Citrus Mutual. Existing moisture, sporadic rain and cloud cover can also help keep in heat.
Andy Coker, an assistant manager for the Limoneria Company farm in Santa Paula, a leading grower of avocados, lemons and oranges, told NBC Bay Area that he would be pulling “all nighters, all weekend probably for the next four or five days,“ trying to keep hundreds of acres of avocado trees warm.
Snow shut a 40-mile stretch of a major highway north of Los Angeles on Thursday afternoon, forcing hundreds of truckers to spend the cold night in their rigs and severing a key link between the Central Valley and Los Angeles.
The California Highway Patrol reopened the Grapevine segment of Interstate 5 some 17 hours later.
After a cold blast in the southwestern U.S., the forecast predicts warmer weather in the coming week. Meanwhile, the Midwest remains entrenched in a deep freeze. The Weather Channel's Greg Forbes reports.
Associated Press writers Gosia Wozniacki in Fresno and Chris Carlson in Orange contributed to this report. NBC Bay Area also contributed reporting.