Annual rainfall in the Bay Area ranges from about 12 inches in the driest inland valleys to more than 50 inches on the wettest coastal ridges. San Francisco averages about 23 inches a year and Oakland about 24. Santa Rosa gets about 32 inches, while San Jose gets only about 14. The pattern depends on distance from the coast, the height of nearby hills and which way those ridges face the incoming storms. Hills that force moist air upward squeeze extra rain out of it, a process called orographic lift. Knowing where you sit on this map helps when choosing a neighborhood, planning an outdoor event or wondering why one town floods while another stays dry.
Which Bay Area Cities Get the Most Rain?
The wettest populated areas are in the North Bay hills and the Santa Cruz Mountains. San Rafael averages about 38 inches a year and Santa Rosa about 32. The hills above Berkeley and Oakland get 26 to 29 inches depending on elevation, and Tilden Regional Park averages about 26. Ben Lomond, in the redwoods of the Santa Cruz Mountains, gets about 50 inches, which makes it one of the wettest towns in the region.
Pacific storms usually arrive from the west and southwest, carrying moist air near the surface. When that air reaches the coastal ranges, it is forced upward, cools and drops extra rain on the windward slopes. Towns just east of a ridge sit in a rain shadow, where the air sinks, warms and dries out. That is why the Berkeley hills get 26 to 29 inches while Walnut Creek, just over the ridge, gets about 20.
Which Bay Area Cities Get the Least Rain?
The driest major Bay Area city is San Jose, at about 14 inches a year. The Santa Clara Valley sits in a partial rain shadow, because the Santa Cruz Mountains wring much of the moisture out of storms before they reach it. Fremont, across the South Bay, gets a similar amount.
Livermore and the rest of the Tri-Valley average 14 to 16 inches, because they sit behind both the coastal ranges and the East Bay hills. That is close to what Los Angeles gets in a typical year. Antioch, in the far East Bay, is drier still at about 12 inches, and nearby Concord is only a little wetter.
Rainfall by Subregion
The North Bay, which covers Marin, Sonoma and Napa counties, is the wettest subregion, with 25 to 40 inches in most towns. Its hills are some of the first high ground that winter storms meet after crossing the Pacific, and many ridges face the incoming storms head-on. Mount Tamalpais gets more than 50 inches a year on its upper slopes.
On the Peninsula, in San Mateo County, the bay-side cities get a moderate 20 to 25 inches, while the Santa Cruz Mountains get 30 to 50. Half Moon Bay on the coast averages about 26 inches. The East Bay is split between 26 to 29 inches in the hills and 15 to 20 in flat bay-side cities like Fremont, Hayward and Union City. San Francisco's 23 inches surprises many people, because the city's rainy reputation comes from how often it rains rather than how much. Measurable rain falls on more than 60 days in a typical year.
Why Rainfall Totals Matter for Bay Area Life
These differences shape daily life in practical ways across the region. Flood risk is highest in the wetter subregions and along creeks that drain steep hills. Wildfire risk runs higher in drier areas, where grass and brush cure earlier in summer. Most of each year's rain falls from November through March, as our guide to the wettest months explains. Because the rain comes in one season, a 40-inch town spends its winters saturated, while a 15-inch town can stay fairly dry.
