Mild, Blustery Storm Passes; Cold Christmas Eve Rain Next
An enhanced image from NOAA's GOES West weather satellite, showing dense plume of water vapor feeding Monday's storm over Northern and Central California. (National Oceanic and Atmospheric Administration)
Update, 8:55 a.m. Tuesday: The storm's heaviest rain has moved south of the central Bay Area, into the Santa Cruz Mountains, the highlands along the Big Sur coast and well beyond. As forecast, the weather system brought gusty winds into the Bay Area overnight, with many locations recording gusts of 40 mph and above. The highest gust reported by the National Weather Service on Tuesday morning: 71 mph at the Big Rock recording station, a ridgetop location above Marin County's Lucas Valley.
Other notable gusts: 62 mph on Atlas Peak, northeast of Napa; 55 mph at Las Trampas Ridge, west of the San Ramon Valley; 51 mph at San Francisco International Airport; 51 mph at the Benicia Bridge; 50 mph at Altamont Pass, east of Livermore.
Our next storm, bringing colder temperatures and lighter rain, is expected to arrive late Wednesday in northern Sonoma County and continue through most of Christmas Eve. Forecasters say about an inch of rain could fall in ridgetop and mountain locations, with a chance of Christmas morning snow on the region's highest peaks. Lowland rainfall totals are expected to be modest -- just one-tenth to one-third of an inch.
The Tahoe Daily Snow reports that ski resorts along the crest of the Sierra picked up as much as 59 inches of snow over the past four days.
The Wednesday-Thursday storm is expected to bring another dumping of snow to the Sierra, with as much as 18 inches expected near the highway passes and even more at higher elevations.
That weather system is expected to be followed by an extended, chilly break between storms, with most of the region forecast not to see precipitation again until early in the new year.
Update, 4:45 p.m. Monday:
After a strangely wet/damp/dry weekend in the Bay Area -- depending on where you were, you got a good soaking or saw hardly a drop of rain -- the Bay Area and much of the rest of Northern California is in for widespread rainfall marked by occasionally heavy downpours and high winds.
The National Weather Service Bay Area office in Monterey says the storm system punching across the coast Monday afternoon will bring rainfall ranging from a half-inch to an inch in areas adjoining San Francisco Bay to 5 inches in the Santa Cruz Mountains, East Bay hills and higher elevations of Marin and Sonoma County. West to northwest winds are forecast to increase to 20 to 30 mph over the higher terrain of Marin and Sonoma counties and the East Bay, with gusts of 50 mph possible.
The latest storm, fed by a relatively dense plume of moisture being driven northeast across the Pacific from the subtropics west of the Hawaiian Islands, is dumping heavy rain over the Sierra foothills -- from 3 inches to 6 inches in some area -- and lots of snow higher up in the mountains. As much as 3 feet of heavy, wet snow could fall on Sierra peaks.
The copious rainfall in the foothills prompted the National Weather Service in Sacramento to issued flash flood watches for areas burned by the Rim and American fires (2013), the King Fire (2014) and the Butte Fire (2015).
North of the Bay Area, the storm has also caused flooding in the Mendocino County city of Ukiah and has led to an advisory that flooding will occur in communities across the county. A flood watch was posted for the southern Mendocino County town of Hopland, where the Russian River is expected to rise dramatically by early Tuesday.
Monday's rain comes on top of totals that, for the northern half of the Bay Area, was a pretty wet weekend.
Precipitation over the weekend, starting in the early hours of Friday morning through Monday morning, ranged from .30 of an inch at San Jose International Airport to 7.29 inches at Mount Tamalpais' Middle Peak recording station. The disparity was starkest on Sunday, when South Bay locations received little or no rain -- .01 inch at San Jose airport -- while Mount Tam saw 4.54 inches.
The main reasons for the difference: The stream of moisture feeding Sunday's daylong rain was focused more to the north of the Golden Gate, and the Peninsula Hills and Santa Cruz mountains wrung out the rainclouds blowing in off the Pacific before they could make it to the Santa Clara Valley.
Monday's storm is expected to move south and east by Tuesday afternoon. Wednesday could see a break in the rain before a less potent but much colder storm arrives on Christmas Eve. If you're planning to be caroling or lighting luminaria, the early forecast suggests that rain may end by early evening. Dry weather is forecast for Christmas Day and at least the first part of the weekend.