Rain expected to fall for the first time in nearly a month

Rain is expected to fall in the Bay Area this weekend, and though it won’t alleviate drought concerns and may not even put a hard end to fire season, forecasters say it couldn’t be more welcome.

“You have to start somewhere,” National Weather Service meteorologist Drew Peterson said Thursday morning.

The Bay Area has not seen measurable rain in almost a month — since Nov. 18 — prompting concerns of another dry. This weekend’s rain won’t come down heavily, though it will be measurable — more so Sunday, Peterson said, when another cold front follows the one that’s expected to hit the North Bay and work its way down late today.

The heaviest rain is expected in the mountains and along the coast, Peterson said. As much as 1¼ inches could fall along coastal areas. Areas in Marin County, southern Napa and the Santa Cruz mountains could get as much as 3/4 of an inch.

The rain in the East Bay and South Bay is expected to be considerably lighter, with about a quarter-inch to half-inch projected for Contra Costa and Alameda counties and one-eighth to a quarter-inch expected in Santa Clara County.

“On Friday into Saturday, we expect the precipitation activity to be pretty light,” Peterson said. “The heavier activity will be Sunday with the arrival of the next cold front.”

The National Weather Service also said it expects new snow in the Sierra this weekend, with 8-12 inches forecast above 6,500 feet from today to Sunday.

Winds in the Bay Area are expected to calm a bit, but a wind advisory remained in effect Thursday along the coastal North Bay.

The National Oceanic and Atmospheric Administration said conditions in the Pacific Ocean continue to indicate a moderate to strong La Niña, a pattern that brings colder water than normal to the surface of the Pacific and often brings less rain for a season than normal. Those conditions are expected to last through March.

“A lot of years with La Niña have a pretty late start to the rainy season,” Peterson said. “So if we see a trend toward wetter weather in later December and through January, that would be on par for La Niña. That said, this has been a particularly dry start.”

Rainfall totals have been miserable to this point. San Francisco has received just half an inch of rain since Oct. 1, 9% of its historical average over that time. San Jose and Oakland are both at just 4% of normal, having received .13 and .17 inch, respectively.

Things have been so dry that on Sunday and Monday, the National Weather Service issued a red-flag warning for most of the Bay Area, sounding the alarm for high fire danger, a rarity during December.

No major fires broke out in the Bay Area, but three significant blazes that started in the dry conditions of Southern California continue to burn.

The unusually arid conditions have been expanding. Overall, 95% of the state’s land was in some level of drought condition, according to the U. S. Drought Monitor, a weekly report from the federal government and the University of Nebraska that came out Thursday. That marks the highest total since March 2016, the final year of California’s historic five-year drought.

Worse, 21% of the state — mostly in the Sacramento Valley and far Northern California — is in “extreme drought,” according to the report.

Northern California has received 91% of its historic average rainfall during La Niña winters since 1954, according to an analysis by Golden Gate Weather Services in Half Moon Bay. There have been 22 such winters since then.