The first, and likely the warmest, of a four-night freeze event occurred the night of Jan. 10 with temperatures dipping into the upper 20s and low 30s in citrus producing areas of California’s San Joaquin Valley (SJV). 

Scattered cloud cover and light winds combined with wind machine protection to elevate grove temperatures to above critical points, mitigating the potential for frost damage.

Cold temperatures averaged in the low 30s materialized in citrus producing areas of Riverside, Ventura, and Imperial counties. Frost protection mechanisms successfully raised temperatures. No damage was sustained. 

The inconsistency of topography in Ventura created pockets of cold temperatures as low as 27 degrees for a few hours. The Coachella, Riverside, and Imperial citrus production areas were critical from about 3a.m. to 8 a.m. in the morning. The sensitivity is much greater since trees and fruit are not conditioned for the cold durations as is SJV production.

A flash rain storm made its way through some SJV areas in the early evening before quickly moving east, leaving some concern for the potential of ice mark on the fruit.  However, if any damage is incurred, it will not manifest for some time. 

Overall, temperatures were manageable with the aid of frost protection mechanisms for the mandarin and Navel crops. In frost episodes, mandarins will typically sustain more damage than the more cold-tolerant Navel, but last night’s cloud cover and the use of wind machines were enough to elevate temperatures above the 32-degree threshold, making damage unlikely.

Some growers ran water yesterday afternoon to warm up ground temperatures in preparation for the cold weather. Many opted to delay running water in anticipation for the colder nights to come. Wind machines started running anywhere from midnight to 2:30 a.m. in warmer areas and will continue through sun-up this morning.

Season-to-date temperatures have been fairly moderate allowing the fruit more time to mature and build up strong sugar content, providing internal frost protection.  However, with 75 percent of the crop still on the tree, growers will utilize frost protection mechanisms this weekend to mitigate potential damage.

Overall, temperatures did not drop as low as originally anticipated, but are forecast to drop into the low 20s over the weekend. Wind machines were utilized last night for an average of 6-8 hours in warm areas, up to 10 hours in the coldest areas.

To date, moderate winter temperatures have allowed this season’s crop to develop a high sugar content which will provide internal protection against frost damage. 

The coldest temperatures are forecast for tonight. Growers are running water and will likely start running wind machines in the early evening.