Arctic Air Has Jack Frost Nipping at Groves : Weather: Rare northwester sends temperatures plunging and puts growers on full alert. Overnight lows in the 20s were forecast for most areas of the county.

A rare blast of arctic air routed Orange County’s normally mild winter climate Wednesday and threatened to damage thousands of acres of crops with the first widespread frost of the winter season.

Throughout the day Wednesday area growers prepared for a second night of chilly weather, readying wind machines, sprinkler systems and thermal coverings called “hot caps” to save strawberry fields, avocado trees, citrus groves and nursery plants.

On Wednesday morning, the low temperatures hovered in the 30s and 40s in most areas of the county, with just a few pockets reporting freezing weather. The county’s lowest temperature of 27 degrees was recorded in San Juan Canyon, just east of San Juan Capistrano on Ortega Highway, according to the National Weather Service.

But as the brunt of the Alaskan cold front hit Wednesday night, temperatures plunged and were expected to drop to the mid-20s in most areas in the early morning hours today.

“A front from the Gulf of Alaska is coming almost straight down the entire West Coast, which is why it’s so cold,” said Weatherdata meteorologist Rick Dittman.

On agricultural lands, predominantly in Irvine and San Juan Capistrano, special machinery to handle cold spells is kept on the premises, growers said. “We’ve got our wind machines fueled up and ready to go,” said Alan Reynolds of Treasure Farms, which leases 5,000 acres of Irvine Co. ranch lands in northeast Irvine to harvest oranges, lemons, grapefruits, avocados and beans.

“We’ll start monitoring temperatures, and as the areas get cold we’ll turn on the machines,” Reynolds said, adding that 2,000 acres of crops were in danger.

Also threatened by the chill are ficus and coral trees at the 280-acre SeaTreeNurseries in east Irvine, where workers were moving trees within range of the wind machines, Executive Vice President Tom Larson said.

“When we have a clear sky, no wind and these (low) temperatures, we’re in store for possible danger,” Larson said. The nursery uses a device called a thermograph to measure temperatures at regular intervals, and to record the duration of high and low readings, Larson added, explaining that the length of a freezing spell determines the amount of crop damage.

The Arctic-born weather system caused problems on other fronts as well, driving about 50 homeless people into the National Guard Armory in Fullerton and creating miserable working conditions for the hundreds of people working to clean up the oil spill in Huntington Beach and Newport Beach.

Farther north, powerful gusts prompted the California Highway Patrol to advise large trucks and “high-profile vehicles” to stay off roads from Newhall to Bakersfield. CHP cars equipped with chains escorted traffic along a 40-mile stretch of the snow-swept Golden State Freeway between Castaic and the northern end of the Grapevine near Frazier Park.

Hazardous sheets of ice and snow kept that section of the freeway, the main link to the San Joaquin Valley, closed between 2:45 and 7 a.m., CHP Lt. Robert Caldwell said. All lanes of the freeway were not completely opened by Caltrans snowplows until 11 a.m. Wednesday, he said.

By afternoon today, the cold front will be moving east and temperatures will start to warm. Highs today are expected to climb to the low 60s in Orange County, with lows tonight in the 40s. Friday, increasing cloud cover from a second Alaskan weather system could bring a chance of rain over the weekend and continued cold, Dittman said.

Orange County typically gets about three widespread freezes each winter, said Harry Otto, a farm adviser with the University of California Cooperative Extension, who noted that Wednesday’s predicted frost was late in the current growing season.

“I don’t want to sound like an old codger who’s been around for years,” Otto said. “But frost-wise, it’s been a relatively good season for us. We usually get more than one frost a year in Orange County.”

Last winter, crop growers sustained more than $30 million in damages that were mostly the result of cold weather, according to figures from the Orange County Farm Bureau.

Staff writer Stephen Braun contributed to this report from Los Angeles

LOW READINGS AT COUNTY STATIONS

Low temperatures expected by this morning at Orange County monitoring stations:

Location Temperature San Juan Canyon (Ortega Highway) 25 Peters Canyon 26 San Juan Capistrano 27 Rancho Mission Viejo 27 Los Alamitos 28 Yorba Linda 28 North Irvine 28 Anaheim 32 Santa Ana 32 Newport Beach 38

Lowest temperatures recorded Wednesday morning:

Location Temperature San Juan Canyon 27 Peters Canyon 29 South Coast 29 North Irvine 30

Other low temperatures

El Toro 39 Anaheim 40 Santa Ana 40 Newport Beach 42

Source: National Weather Service