A Pacific storm system spreading across Northern California this weekend is delivering a welcome drenching to parts of the drought-stricken state, dumping copious amounts of rain on the coastal range north of San Francisco and several feet of snow on the Sierra Nevada.
More than 11 inches of rain had soaked one Marin County peak by Saturday afternoon, and another weather station in the coastal mountains recorded more than 7 inches of rain. Parts of Sonoma County received 7 to 9 inches, prompting authorities to issue flash flood warnings.
The storm system, which arrived Thursday and was expected to last through tonight, was part of an atmospheric river, or “pineapple express,” a band of atmospheric moisture from the tropical Pacific Ocean that opens up the faucets when it slams into California’s mountains.
Atmospheric rivers typically deliver one-third to one-half of the West Coast’s precipitation. But an abnormally stubborn high-pressure ridge parked off the coast has blocked storms for most of this parched winter, leaving California in the grip of one of the worst droughts in the modern record.
The weekend dousing should put a dent in the drought. But the state is so far behind in rainfall and snowfall that it would take many more storms to push precipitation levels back to normal.
“I don’t think this is going to be a drought-buster,” said Bob Benjamin, a National Weather Service forecaster in San Francisco. “But it’s certainly going to diminish the deficit.”
Rainfall amounts were less in the Central Valley, and the storm did not reach Southern California. But it was expected to drop an additional 2 to 5 inches of rain north of San Francisco by the time it moves out Monday morning.
The Sierra range north of Yosemite National Park should get a total of 2 to 3 feet of heavy, wet snow, not the kind that skiers like but fine for supplementing the state’s record-low snowpack.
“It’s very good for California’s water supply,” said Darren Van Cleave, a National Weather Service meteorologist in Sacramento. “We need it badly.”
Forecasters are hopeful the arrival of a full-blown pineapple express may signal a return of more typical winter weather. “It does appear that we’re getting back to a normal pattern,” Benjamin said.
Last year was the driest on record in California, and last month was the driest January. State officials have declared a drought emergency and announced delivery cuts to prevent the state’s biggest reservoirs from emptying.