California climate varies from Mediterranean to subarctic. Much of the state has a Mediterranean climate, with cool, rainy winters and dry summers. The cool California Current offshore often creates summer fog near the coast. Further inland, one encounters colder winters and hotter summers.

Northern parts of the state average higher annual rainfall than the south. California's mountain ranges influence the climate as well: some of the rainiest parts of the state are west-facing mountain slopes. Northwestern California has a temperate climate, and the Central Valley has a Mediterranean climate but with greater temperature extremes than the coast. The high mountains, including the Sierra Nevada, have a mountain climate with snow in winter and mild to moderate heat in summer.

The east side of California's mountains has a drier rain shadow. The low deserts east of the southern California mountains experience hot summers and nearly frostless mild winters; the higher elevation deserts of eastern California see hot summers and cold winters. In Death Valley, the highest temperature in the Western Hemisphere, 134 °F (56.6 °C), was recorded July 10, 1913.