Gilroy's climate strikes a pleasant balance between hot and cold, wet and dry, making it perfect for agriculture and recreation. Nestled between the Diablo and Santa Cruz mountains in the Santa Clara Valley, Gilroy residents enjoy mild temperatures, while missing most of the coastal fog. A state climatology report says up to 70 percent of Gilroy's days are sunny, with average rainfall of about 19.11 inches. The proximity of the Pacific Ocean keeps temperatures uniform. The average annual temperature is 62.8 degrees, although it is not unusual for summer readings to top 100. The average July high temperature is near 90. Winter temperatures drop to an average of 57 degrees in January. All-time winter lows have plunged into the 20s, with the 1st freeze usually coming in November. The average date of the last freeze is around March 1.
The agricultural growing season ranges from 300 to 350 days a year. The average relative humidity readings reach 90 percent or more at night during the winter, but drop to around 60 percent during the day. In the summer and fall, humidity reaches 70 percent at night and 40 percent during the day. Winds out of the northwest are usually light to moderate, up to 20 miles an hour.
Earthquake activity is not uncommon, as Gilroy sits between two active faults. The Calaveras Fault runs through the eastern foothills, and the Sargent Fault runs along the western edge of the valley. The Loma Prieta quake in October 1989 was centered 15 miles northwest of Gilroy, registering 7 on the Richter Scale. A 6.2 quake hit Morgan Hill in April 1984.