Meteorologists warn of 'above-average rainfall' during busy travel period in California

National Weather Service meteorologists are eyeing a period of significant rainfall starting next week and persisting throughout the remainder of the month as a storm system makes its way toward the California coastline; the storm could lead to wet conditions in and around the Bay Area that may impede on holiday travel. 

The data comes from the climate prediction center’s 8-14 day precipitation outlook, and while a lot of unknowns remain — specifically in terms of rainfall amounts, timing and location — the system will likely arrive by Dec. 16 and increase in intensity through Dec. 20, said Roger Gass, a meteorologist for the weather service’s Bay Area office. 

“We don’t have a lot of specifics this far out, but we are highly confident that we will see above-average rainfall for this time of year,” he said. “Southern California is expecting to get the brunt of this system, but the Pacific Northwest likely won’t see nearly as much.” 

December and January are typically the wettest months of the year for San Francisco, December being the wettest, with 4.76 inches of rain falling on average, Gass said. Last year, an atmospheric river peaked over the Bay Area on New Year’s Eve, resulting in the second-wettest day in San Francisco since the city began recording rainfall totals in 1849. In 24 hours, San Francisco’s downtown gauge measured 5.46 inches, nearly breaking the Nov. 5, 1994, record of 5.54 inches. The National Weather Service also reported that its gauge at San Francisco International Airport had recorded 20.3 inches of rain since Oct. 1, surpassing the average for the water year, a 12-month period that runs from Oct. 1 to Sept. 30. The site typically records 19.64 inches in a water year on average. 

Still, Gass said, “it’s too soon to say if this will be like the record rainfall we saw last year.” Chances of rain and unsettled conditions increase over the Bay Area as early as this weekend; forecasters will continue to watch the system and share more information once they know more.

“When we reach the three-day mark, we’ll definitely have more details on those amounts,” Gass said. 

People are encouraged to take advantage of the clear and dry conditions this week and clear debris from their gutters and storm drains (temperatures are going to average in the lower 60s and even climb up to the lower 70s by Thursday and Friday in the South Bay). In the event of travel-related impacts when the rain does arrive, Gass advised that people make sure they allow plenty of time to reach their destination and drive slowly and carefully. 

“If things do get wetter, we should be prepared for that,” he said.