Flood in San Mateo County, California

CHP reported flash flooding of US Highway 101 at Oyster Point Road in South San Francisco at 5:58 AM. By 10:58 AM, the entire roadway had flooded and the highway was closed. The flooding caused traffic backups and diversions with Interstate 280 as the alternate. The northbound lanes were reopened around 8 PM and the southbound lanes around 9 PM.

An atmospheric river impacted the Bay Area on December 31st, resulting in significant rainfall across the San Francisco Bay Area. Initial forecasts called for the most intense rainband to progressively move south towards the Central Coast as the day went on. However, the morning of the 31st, a surface low developed west of San Francisco, and the river stalled over the Bay Area. This resulted in significant rainfall totals for many Bay Area sites. Most notably, downtown San Francisco received 5.46 inches of rain on the 31st, the second wettest day on record. The Oakland Museum received its wettest day since records began in 1970, with 4.75 inches of rain.