It's edging toward midnight and John Gless is keeping a wary eye on the thermometer as he patrols his family's 450 acres of citrus orchards outside Hemet.
The temperature hovers just above 30 degrees as he maneuvers his Ford F-250 pickup through the dark canyons between 18-foot trees of Valencia and navel oranges.
A few degrees colder, as the forecast predicts, and the millions of dollars of citrus dancing in his headlights will start to freeze.
"You worked hard all year to get your crops, and there's a chance you'll lose it all tonight," said 29-year-old Gless, a fourth-generation citrus farmer. "I think there's a good chance it's gonna freeze."
Gless and citrus farmers like him across the state have been up all night since Thursday, when arctic winds began pushing down a cold front that threatens the $1 billion in oranges, lemons, tangerines and grapefruit still on trees in California, the nation's largest producer of fresh citrus.
A high-pressure zone sitting off the Pacific Coast has channeled a blast of cold air from the Gulf of Alaska down the backbone of the state. Temperatures on Saturday night were expected to dip as low as 25 degrees, triggering freeze warnings across Southern California.
"It's not unusual for us to get these cold snaps this time of year, but it's one of the colder ones we've had in a while," said Curt Kaplan, a meteorologist with the National Weather Service's Oxnard office.
Starting Monday, cold Santa Ana winds will sweep in from the desert, keeping temperatures low but stirring up the air enough to eliminate most of the threat to the citrus crop. By Wednesday, temperatures should begin to rise.
"These next few nights will be extremely critical nights," said John Nelsen, president of California Citrus Mutual, an association of the state's 3,900 citrus growers, the majority of which are family farmers.
The year had been off to a good start, with a particularly flavorful crop of mandarins and good sugar content across the state. The association has sold up to $300 million in citrus already, with another $1 billion still on the trees.
"We were looking at a very profitable year," Nelsen said.
But a cold snap can change that in hours. In January 2007, citrus growers lost 60% of the state's crop to freezes. In 1998 it was 85%. The worst season in memory was the Christmas freeze of December 1990, when a week of temperatures in the teens defoliated the orchards, leading to a total loss for that season and the one after, Nelsen said.
It's those memories that keep citrus farmers like Gless up patrolling their orchards all night like an expectant father pacing outside the delivery room.
Gless' great-grandfather raised citrus and melons in Texas. His grandfather moved the family to El Toro, Calif., and slowly bought up acreage in Riverside, Hemet and the Coachella and Central valleys.
Gless grew up in Riverside and learned to drive a tractor at 8. Patrolling the orchards during winter cold snaps has become a way of life, one his wife and 2-year-old son are still getting used to. As he wends his way through the dark orchards in Hemet, his father is doing the same in the Central Valley while his grandfather monitors the frost alarms from Riverside.
When low temperatures are forecast, they'll order extra water and run it all night, helping the ground to hold on to some of the heat it absorbed during the day. With 3 1/2 acre-feet of water needed for every acre of land, that can quickly get costly.
Each of their citrus ranches has an automated thermometer that can be called from the warmth of bed. But small changes in topography can mean a swing of several degrees across an orchard of a few hundred acres.
That leads to long, tedious nights of patrolling and waiting for the temperature to hit that magic number for citrus farmers: 29 degrees.
When it does, Gless springs into action. Thanks to air-quality rules, the smudge pots citrus farmers once used to burn sooty diesel fuel are a thing of the past. Instead, Gless and his crew will fire up dozens of giant propane-powered wind machines. With one machine for every 10 acres of grove, it can take hours to get them all started.
The wind they create stirs up the inversion layer, mixing the cold air that settles low with the layer of warmer air that sits atop it like a blanket.
Taken together, the water and wind can raise the temperature in an orchard by as much as five degrees, enough to save a year's worth of work from being sold for juice.
It will be a few days before Gless and his fellow citrus growers cut into their fruit and look for the signs of freezing that tell them if their measures worked.
jason.felch@latimes.com
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