Weather watchers can follow the freeze temperatures around the groves near Reedley, Ivanhoe, Terra Bella and Lindsay on the California Citrus Mutual web site.
Joel Nelsen, president of the Exeter-based group, said the numbers will be updated regularly throughout the day.
He said growers are running water through their irrigation systems to moisten and warm the ground. As temperatures dip, they will use wind machines to circulate the warmer ground-level air, hoping to protect the fruit from a heavy frost.
The San Joaquin Valley is the largest producer of citrus in California.