Weather Averages in San Jose
San Jose, like most of the Bay Area, has a Mediterranean climate (Köppen Csb). San Jose has an average of 301 days of sunshine and an annual mean temperature of 60.5 °F (15.8 °C). It lies inland, surrounded on three sides by mountains, and does not front the Pacific Ocean like San Francisco. As a result, the city is somewhat more sheltered from rain, giving it a semiarid feel with a mean annual rainfall of 15.82 inches or 401.8 millimeters, compared to some other parts of the Bay Area, which can receive about three times that amount.
Like most of the Bay Area, San Jose is made up of dozens of microclimates. Because of a more prominent rain shadow from the Santa Cruz Mountains, Downtown San Jose experiences the lightest rainfall in the city, while South San Jose, only 10 mi (16 km) distant, experiences more rainfall, and somewhat more extreme temperatures.
The monthly daily average temperature ranges from around 50 °F (10 °C) in December and January to around 70 °F (21.1 °C) in July and August. The highest temperature ever recorded in San Jose was 109 °F (42.8 °C) on June 14, 2000; the lowest was 19 °F (−7.2 °C) on December 22–23, 1990. On average, there are 2.7 mornings annually where the temperature drops to, or below, the freezing mark; and sixteen afternoons where the high reaches or exceeds 90 °F or 32.2 °C. Diurnal temperature variation is far wider than along the coast or in San Francisco but still a shadow of what is seen in the Central Valley.
With the light rainfall, San Jose and its suburbs experience about 300 fully or partly sunny days a year. Rain occurs primarily in the months from November through April. During the winter and spring, hillsides and fields turn green with grasses and vegetation, although deciduous trees are few. With the coming of the annual hot summer dry period, the vegetation dies and dries, giving the hills a golden cover which, unfortunately, also provides fuel for grass fires.
Measurable precipitation falls in downtown San Jose on an average of 59 days a year. “Rain year” precipitation has ranged from 4.83 inches (122.7 mm) between July 1876 and June 1877 to 30.30 inches (769.6 mm) between July 1889 and June 1890, although at the current site since 1893 the range is from 5.77 inches (146.6 mm) in “rain year” 1975–76 to 30.25 inches (768.3 mm) in “rain year” 1982–83. The most precipitation in one month was 12.38 inches (314.5 mm) in January 1911. The maximum 24-hour rainfall was 3.60 inches (91.4 mm) on January 30, 1968. Although summer is normally quite dry in San Jose, a very heavy thunderstorm on August 21, 1968, brought 1.92 inches (48.8 mm) of rain, causing some flooding.
The snow level drops as low as 2,000 ft (610 m) above sea level, or lower, occasionally coating nearby Mount Hamilton and, less frequently, the Santa Cruz Mountains, with snow that normally lasts a few days. Snow will snarl traffic traveling on State Route 17 towards Santa Cruz. Snow rarely falls in San Jose; 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 (0.076 m) on car and rooftops. The official observation station measured only 0.5 inches (0.013 m) of snow.