Bay Area Forecasts First Fall Rain as Coast Faces Flood Risk

After months of dry conditions and recent heat that prompted red flag warnings in the North Bay, the Bay Area is preparing for its first fall rainfall, with showers expected to begin Tuesday and continue intermittently through at least Thursday morning. The National Weather Service attributes the changing conditions to a low-pressure system moving in from the Pacific Ocean and settling over the region.

Rainfall across the Bay Area is expected to remain light, with most locations receiving between 0.05 and 0.15 inch. The Santa Cruz Mountains and parts of the East Bay could receive up to 0.25 inch, according to National Weather Service meteorologist Matt Mehle.

Light showers are forecast to reach the Central Coast on Tuesday morning before moving north. San Francisco could experience rainfall Wednesday morning, while precipitation is expected to continue intermittently into Thursday, according to the weather service.

Mehle said the timing of the showers could bring rain to San Francisco during the middle of the week.

“Wednesday morning, people in San Francisco could wake up to some light rain moving through,” Mehle said. “We have rain in the forecast all the way into Thursday.”

The expected precipitation marks the region's first rain in months. Although totals are forecast to be modest, the initial rainfall could affect driving conditions after an extended dry period.

Mehle cautioned that accumulated oil on road surfaces could create hazards when rain arrives.

“This will wash the roads,” Mehle said of the light rain forecast. “We do urge people to have some caution on roadways because oil that has accumulated could cause issues.”

Further south, the Central Coast could receive up to 0.75 inch of rain, substantially more than the forecast for most Bay Area locations. The National Weather Service also forecasts a risk of thunderstorms of up to 20% in the area as the unsettled weather moves through.

Heavier rainfall could pose a flash flood threat around Big Sur and nearby areas affected by the Timber and Plaskett wildfires. Burned terrain can allow water to run rapidly across the surface, potentially carrying debris downhill when rainfall rates exceed local thresholds.

The National Weather Service highlighted the danger for properties situated below wildfire burn scars in its forecast discussion.

“If rainfall rates exceed their thresholds, the water will slip right off the surface, resulting in burn scar debris flows, which may lead to flash flooding. If your home is downslope of these burn scars, now is the time to prepare for the possibility of an emergency,” the forecast discussion said.