The National Weather Service has issued a flood watch for the Bay Area and California’s Central Coast due to an atmospheric river event that is predicted to cause “excessive rainfall” later this week. The flood watch will take effect on Thursday afternoon and last until Sunday morning. The heaviest rainfall is expected on Thursday night into Friday morning. Most parts of the Bay Area are expected to receive between 1.5 and 4 inches of rainfall in lower-elevation areas, and higher amounts are anticipated in coastal mountain regions. The NWS meteorologist, Jeff Lorber, has stated that certain areas could receive between 6 to 8 inches of rain over the weekend.
On Tuesday, the National Weather Service’s Weather Prediction Center indicated a “slight risk” of flash flooding for the Bay Area. However, the risk increased to “moderate” with at least a 40% chance that the amount of rainfall from Thursday to Friday could exceed flash flood guidance. Evacuations, downed trees, and power outages are possible and people should be prepared in advance. Due to persistent rainfall over the past few weeks, soil saturation will result in runoff entering streams and roads, creating travel hazards, especially around poor drainage areas. Travel delays and possible road closures are expected where creeks and streams overflow their banks. Mudslides and debris flows are also possible in areas with steeper terrain, such as the Santa Cruz Mountains.
In addition, powerful gusts of wind of up to 45 mph are expected, which may exacerbate these conditions throughout most of the Bay Area. Gutters should be cleared, and any debris that could be quickly carried away in heavy rain should be removed. People should check with the California Highway Patrol, Caltrans, and local authorities for guidance on road closures and possible evacuation. Lorber recommends that people stay home on Friday if they don’t have to travel.
Cold temperatures are also expected, and they could come close to breaking previous record lows, especially in San Francisco and Oakland. Lorber advises that people without adequate shelter should seek warming centers or areas that may protect them from the cold. A wet pattern is likely to continue in the Bay Area through at least the middle of next week, with the potential for flooding in rivers and streams. The Bay Area is nearing the end of the rainy season; Lorber believes that eventually, drier conditions will occur. However, flooding concerns should still be taken seriously.