A looming storm is likely to bring the heaviest rain in more than six months to San Francisco on Friday, with another system to follow Sunday, the San Francisco Chronicle reported.
Rainfall totals of 1 to 2 inches are forecast for the Bay Area through Monday morning, along with two rounds of breezy conditions. Most of the rain will fall in a short time, with the highest amounts in the North Bay mountains and lighter totals in the Santa Clara Valley, the Chronicle reported. Water could easily puddle on roadways. The combination of heavy rain and storm surge from strong winds could flood low-lying parts of Marin County, with high tide predicted just before 1 p.m. A coastal flood advisory is in effect. Southerly gusts up to 40 mph, the strongest so far this season, will peak before the heaviest rain hits. Choppy water on San Francisco Bay could affect ferry crossings, and branches can snap more easily than in a later-season storm because many trees still have their leaves.
The front should clear the Bay Area by the evening commute, then move toward the Sierra Nevada and rapidly lower the snow line. Blizzard-like conditions are possible over Donner Summit as early as Friday afternoon, and the Chronicle advised postponing cross-Sierra travel until Saturday. Temperatures in the Bay Area will drop to the 50s in the wake of the front, with lows falling to the 40s in the inland valleys. Timing may shift by a few hours, but there is high confidence that a bulk of the rain in the Bay Area will fall during daylight hours Friday, the Chronicle reported.
Saturday looks calmer in the atmosphere, but a large swell is expected to ramp up Friday night and peak Saturday morning, with waves of 20 to 30 feet forecast at most beaches. The National Weather Service is warning of life-threatening conditions at the beach; that coastal hazard has already been the subject of a separate advisory story. Another system Sunday could mirror Friday's impacts, though slightly weaker, arriving in the late afternoon rather than midday. Rainfall totals of a quarter-inch to three-quarters of an inch Sunday would bring the two-storm total to 1 to 2 inches for most of the Bay Area, the Chronicle reported, with more wet weather possible next week.