Light rain has begun falling across the North Bay on Monday afternoon, with steady precipitation reported in Healdsburg and Santa Rosa and light showers as far south as San Rafael for the Monday evening commute.
Rain will continue throughout the Bay Area for the rest of Monday evening, reaching San Francisco and Oakland sometime after 8 p.m. Totals are trending higher than originally forecast as a low pressure system slowly drifts down the California coast. Localized totals near one inch are possible in parts of the North Bay by Tuesday morning.
The heaviest stretch in the North Bay arrives between 8 p.m. Monday and 3 a.m. Tuesday, with showers tapering by 8 a.m. in the morning. In San Francisco, the urban East Bay corridor and the Peninsula, steadier rain should fall between 10 p.m. and 4 a.m. Tuesday, with the heaviest activity from 2 to 5 a.m. and showers on the way out by 9 to 10 a.m. Pacifica, Half Moon Bay, and Daly City are on the same rainfall timeframe, with the wettest stretch in the predawn hours.
Rainfall totals will range between 0.25 to 0.50 inches across the North Bay, with interior Marin, Sonoma, and Napa mountain totals approaching an inch. From the Golden Gate south through the Peninsula and into Alameda County, totals should range between 0.10 to 0.25 inches.
In any case, the Tuesday morning commute will likely start out damp, with a drying trend by the late morning.
Behind the system, Tuesday brings slow clearing through the morning, with partial sunshine developing by the afternoon, especially inland and possibly even in San Francisco. Highs will hold in the mid-60s around the bay and climb into the 70s inland.