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 first 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.