Some San Joaquin Valley citrus growers turned on their wind machines in the early morning hours of Dec. 4 as the early wave of a cold front hit the California region.

“We’re still expecting the coldest temperatures to hit tonight,” said Alyssa Houtby, director of public affairs at Exeter-based California Citrus Mutual on Dec. 4. “It was in the low 30s last night and some of the outlying areas did get into the upper 20s. But we aren’t hearing of any devastating cold temperatures.”

The tipping point for damage to navels and lemons is 28 degrees. Frost protection measures like running water and wind machines can add three or four degrees to keep fruit above the threshold.

Mandarins would face the brunt of any damage, given their threshold of 32 degrees.

Forecasts vary through the valley. In Reedley, Calif., for one, the National Weather Service is predicting lows of 21 degrees on the nights of Dec. 4-5. The Dec. 6 low is projected at 30 with a chance of snow. Warming is expected by the end of the weekend. Lows in Fresno were forecast at 28 to 29 degrees Dec. 4-5; Porterville, 25 to 26.

But it’s not just about how low the temperature gets — the duration of cold and the location of groves matters. About four hours below the thresholds would damage fruit.

The Salinas Valley also had freezing temperatures Dec. 4. Vegetable production has already transitioned to the Arizona and California desert regions.

In Oxnard where California strawberry production is focused from December to April, the National Weather Service forecast lows of 37 degrees, above normal minimum requirements for the fruit. Growers could be spared by their proximity to the ocean, but had frost protection measures ready if needed.

“One grower I talked to had their wind machines in place and they were servicing others in the Oxnard plain to be ready just in case,” said Carolyn O’Donnell, communications director for the Watsonville-based California Strawberry Commission. “The guys in Oxnard will have temperature sensors that alarm their smartphones to let them know when temperatures do drop enough to institute frost protection.”