California ended 2022 with a heavy rainfall event that brought flooding to San Francisco and surrounding areas, resulting in landslides, inundated roads and evacuation orders. The second highest daily rainfall total on record fell on New Year’s Eve in downtown San Francisco (with records extending back to 1949), with 5.46in recorded. This is more than 25% of the annual average rainfall, and only 0.08in short of the all-time record set in November 1994.
Recent heavy rains have been part of an atmospheric river event – where a conveyor belt of warm, moist tropical air is able to interact with and feed into mid-latitude storm systems, greatly enhancing rainfall potential.
Due to an anomalously dry start to 2022, San Francisco had experienced about 20% of normal rainfall totals through early October. Prior to this latest event, rainfall totals since October were close to average, meaning that – despite the wet end to December – San Francisco ended 2022 with only approximately two-thirds of the annual average rainfall.
After a brief lull in the heavy rainfall to start this week, a new atmospheric river is expected to hit California from Wednesday onwards, with further heavy rain, strong winds and mountain snow expected. About 3in of rain is forecast with the next storm system for lowland areas around San Francisco Bay, with totals exceeding 6in in the coastal mountains to the north and south.
