California citrus growers are sweating a hard freeze that has blanketed the nation's largest fresh-fruit market in the midst of harvest.

The National Weather Service said temperatures dropped to as low as 19 degrees in some regions early Tuesday. It forced orange farmers to fire up wind machines and flood groves with water to keep bitter cold air from settling.

"Every winter is weird," said Dean Thonesen of Sun West Fruit Company east of Fresno, where mandarins and navel oranges are being harvested. "We'll continue harvesting in the fields that have water or wind machines, but the others we'll have to evaluate."

Oranges begin to suffer at about 28 degrees. Thonesen said his mandarin fields are in a pocket where temperatures dipped below the critical mark.

"It will be a week before we see what damage there may or may not be," he said.

The overall outlook is good for those in areas where the temperatures stayed in the mid-20s, said Bob Blakely, director of industry relations for the growers' co-op California Citrus Mutual.

"Growers reported damage north of Fresno County, but we don't want to give the impression it's widespread," he said.

Officials with the Fresno County Agricultural Commissioner's Office are sampling fruit from the coldest regions looking for signs of freeze damage. They use thermal imaging devices to pinpoint the areas where temperatures dipped below the danger point for the longest periods of time.

NOTE 12160 !!!!

Deputy Commissioner Fred Rinder said officials will examine fruit Friday in affected areas to see if the freezing burst the tiny juice-storing cells inside the oranges that leads to dryness. County agricultural commissioners can withhold damaged citrus from the fresh-fruit market.

"Growers call us the crop cops," said Rinder, adding that it's one of the more odious parts of his job.

Even with another freeze predicted for Tuesday night, the weather still isn't as cold as the freeze of 2007 that caused widespread damage to California's citrus crop. Temperatures were expected to drop to freezing in citrus areas by 10 p.m. Tuesday, which could signal a long night for growers. By Thursday, a storm that is predicted to hit Northern California should bring slightly warmer temperatures.