Flood advisories are in effect across the Bay Area as a storm system moves through the region this evening, according to the National Weather Service.

The biggest storm to hit the Bay Area in roughly seven months began to douse much of California on Monday afternoon, slowing motorists, dropping snow in the Sierra Nevada, and providing a clear signal that the winter rainy season has begun.

A cold front from the Gulf of Alaska was expected to bring half an inch to 1 inch of rain for most Bay Area cities, with up to 2 inches in the Santa Cruz Mountains and Big Sur by the time it was all over.

The steady rain began around lunchtime Monday, hitting the North Bay first and working its way south. Forecasters said it was likely to continue overnight into early Tuesday, stopping around mid-morning as the system passes through to the east.

The average monthly rainfall total for October in San Francisco is 0.94 inches, 0.88 in Oakland and 0.80 in San Jose, meaning this storm has the potential to bring a month’s rain in two days. While there have been huge storms occasionally in October, like in 1962 and 2021, it’s not normally a rainy month.

Pedestrians are reflected in shop windows as they walk in the rain in downtown Palo Alto, as a storm arrives in the Bay Area on Monday, Oct. 13, 2025. (Dai Sugano/Bay Area News Group) 
Cars make their way along a flooded High Street near Interstate 880 in Oakland, Calif., on Monday, Oct. 13, 2025. (Jane Tyska/Bay Area News Group) 
A shopper at Broadway Plaza shields themself from the rain in Walnut Creek, Calif., on Monday, Oct. 13, 2025. A rainstorm is set to arrive in the Bay Area Monday afternoon and stay through Tuesday, bringing with it showers and a chance of thunderstorms. (Jose Carlos Fajardo/Bay Area News Group) 
Police respond to an accident as traffic backs up near the Fruitvale Avenue exit in Oakland, Calif., on Monday, Oct. 13, 2025. (Jane Tyska/Bay Area News Group) 
People spend the morning enjoying themselves before the expected rain arrives later this afternoon while at Hidden Lakes Park in Martinez, Calif., on Monday, Oct. 13, 2025. A rainstorm is set to arrive in the Bay Area Monday afternoon and stay through Tuesday, bringing with it showers and a chance of thunderstorms. (Jose Carlos Fajardo/Bay Area News Group) 
Pedestrians walk in the rain in downtown Palo Alto as a storm arrives in the Bay Area on Monday, Oct. 13, 2025. (Dai Sugano/Bay Area News Group) 
Mount Diablo is surrounded by clouds as hawk flies in the horizon at Hidden Lakes Park in Martinez, Calif., on Monday, Oct. 13, 2025. A rainstorm is set to arrive in the Bay Area Monday afternoon and stay through Tuesday, bringing with it showers and a chance of thunderstorms. (Jose Carlos Fajardo/Bay Area News Group) 
Michelle Lemos, of San Ramon, walks in the rain while holding her water lilies umbrella while shopping at Broadway Plaza in Walnut Creek, Calif., on Monday, Oct. 13, 2025. A rainstorm is set to arrive in the Bay Area Monday afternoon and stay through Tuesday, bringing with it showers and a chance of thunderstorms. (Jose Carlos Fajardo/Bay Area News Group) 

A pedestrian walks in the rain in downtown Palo Alto as a storm arrives in the Bay Area on Monday, Oct. 13, 2025. (Dai Sugano/Bay Area News Group)