San Jose, California, like most of the Bay Area, has a Mediterranean climate. Unlike San Francisco, California, which is exposed to the ocean or Bay on three sides and whose temperature therefore varies relatively little year-round and overnight, San Jose, California lies farther inland, protected on three sides by mountains. This shelters the city from rain and makes it more of a semiarid, near-desert area, with a mean annual rainfall of 14.4 inches (366 mm), compared to some other parts of the Bay Area, which can get up to four times that amount. It also avoids San Francisco’s omnipresent fog most of the year.
However, temperatures are generally moderate. January’s average high is 61 °F (16 °C) and average low is 44 °F (6 °C), with overnight freezes several nights each year; July’s average high is 86 °F (29 °C) and average low is 59 °F (14 °C), with heat exceeding 100 °F (38 °C) several days each year. The highest temperature ever recorded in San Jose was 109 °F (42.8 °C) on June 14, 2000; the lowest was 17 °F (-8.3 °C) on January 9, 1920 and January 10, 1920. Temperatures between night and day can vary by 30 or 40 °F (17 to 22 °C). Temperatures exceed 90 °F (32 °C) on an average of 18.3 days annually, and drop to 32 °F (0 °C) or lower on an average of 1.6 days annually. Temperatures drop below 40°F on average of 4.6 days annually. Soil temperatures in Silicon Valley always rise above 60 °F (16 °C) year round, making warm-season crops available to grow all year round, especially in San Jose, Santa Clara, Sunnyvale, Los Altos, Los Gatos, Monte Sereno, Cupertino, Saratoga, and Milpitas, California.
With the light rainfall, San Jose, California and its suburbs experience over 300 days a year of full or significant sunshine. Rain occurs primarily in the months from October through April or May, with hardly any rainfall from June through September. During the winter, hillsides and fields turn green with grasses and vegetation, although deciduous trees are bare; with the coming of the annual summer dry period, the vegetation dies and dries, giving the hills a golden cover, which also provides fuel for frequent grass fires.
Measurable precipitation falls in downtown San Jose, California on an average of 50 days a year, many times only for part of the day. Annual precipitation has ranged from 6.12 inches (155 mm) in 1953 to 32.57 inches (827 mm) in 1983. The most precipitation in one month was 10.23 inches (260 mm) in February 1998. The maximum 24-hour rainfall was 3.60 inches (91 mm) on January 30, 1968. Although the summer is normally quite dry in San Jose, California, a very heavy thunderstorm on August 21, 1968, brought 1.92 inch of rain, causing some localized flooding.
The snow level drops as low as 2,000-ft (610 m) above sea level, or lower, occasionally each winter, coating nearby Mount Hamilton, and less frequently the Santa Cruz Mountains, with snow that normally lasts a few days. This sometimes snarls traffic traveling on State Route 17 towards Santa Cruz. Snow occasionally falls in San Jose, California, but until recently, the most recent snow to remain on the ground was on February 5, 1976, when many residents around the city saw as much as 3 inches (7.6 cm) on car and roof tops. The official observation station measured only 0.5-inch (13 mm) of snow. However, in March 2006, a smaller amount, up to one-inch (2.5 cm) of snow fell in downtown San Jose, California as well as other areas around the city at elevations of only 90 feet (27 m) to 200 feet (61 m) above sea level.
Like most of the Bay Area, San Jose, California is made up of dozens of microclimates. Downtown San Jose experiences the lightest rainfall in the city, while South San Jose, only 10 miles (16 km) distant, experiences more rainfall and slightly more extreme temperatures.