An end to a lengthy dry spell that has made this December one empty of rain in the Bay Area but heavy with tule fog more common for the Central Valley is about at hand, according to the National Weather Service.
The bigger impact on the month-long pattern is not expected to hit heavily until later in the week, if then.
“We’re probably going to have some occasional light precipitation late (Monday) into (Tuesday) and then later in the week,” NWS meteorologist Rick Canepa said. “The much better chance for a more impactful system is next week. There’s a large-scale trough setting up over the Northeastern Pacific. Now if that large-scale pattern backs up a little bit and retrogrades, it might not be as wet. We’ll have to wait and see how that goes.”
Until then, temperatures are expected to remain cold — the overnight low’s were in the low 40s in most of the region Monday and dipped into the 30s in Livermore — and fog is likely to keep blanketing the region.
Nevertheless, the stage is set for the region to see it’s first measurable rain since Nov. 21. Most of it is anticipated to fall in the North Bay area of the region, and Canepa said no more than a quarter-inch is anticipated to fall. That could leave enough for a some drops to hit closer to the South Bay and East Bay on by Tuesday but no more than that.
Concurrently, the old pattern that has created tule fog in many areas of the region will hold on for at least a couple of more days as the new system develops, Canepa said. A dense fog advisory in effect until 11:30 a.m. Monday included the East Bay interior valleys out to the Delta, the Santa Clara Valley, the San Francisco Bay Shoreline, Monterey Bay, the Salinas Valley, San Pablo Bay and San Francisco Bay.
Visibility on Monday morning was reported to be only a half-mile at the Oakland San Francisco Bay Airport and a quarter-mile in Livermore.
Eventually this week, the establishment of the new pattern is expected to help bring back the ocean influence that is typical of the Bay Area and that will help end the tule fog, Canepa said. That could happen by Friday, when the second system that Canepa is expected to have it’s biggest impact next week may bring even more rain.