The first, and likely the warmest, of a four-night freeze event occurred last night with temperatures dipping into the upper 20s and low 30s in citrus-producing areas of the San Joaquin Valley. Scattered cloud cover and light winds combined with wind machine protection elevated grove temperatures to above critical points, mitigating the potential for frost damage.
Cold temperatures averaging in the low 30s also materialized in citrus producing areas of Riverside, Ventura, and Imperial counties, but again, frost protection mechanisms were successful at raising temperatures and no damage was sustained. The inconsistency of topography in Ventura created pockets of cold temperatures, as low as 27 degrees for a few hours. Coachella, Riverside, and Imperial production areas were critical from about 3 a.m. to 8 a.m. this morning. Their sensitivity is much greater inasmuch trees and fruit are not conditioned for the cold durations as is San Joaquin Valley production.
A flash rain storm did make its way through some producing areas of the San Joaquin Valley 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 both 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 did start running water yesterday in the late afternoon to warm up ground temperatures in preparation for the cold weather. But, many opted to hold off 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% of the crop still on the tree, growers will be utilizing 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 to 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 preparing by running water and will likely start running wind machines in the early evening.