Remember winter? It’s about to come roaring back.
A series of storms will rumble into California this weekend, bringing strong winds, 2 to 3 inches of rain to Lake County and most Bay Area cities, 4 to 7 inches of rain in the coastal mountains and up to 2 feet of new snow in the Sierra Nevada by Monday morning, forecasters said Thursday.
The storms threaten to down trees and knock out power in some places, but they should help boost seasonal rainfall and snowpack totals across Northern California back to historic averages after a dry, hot February. And although they won’t end the state’s four-year drought, the approaching deluge will continue to ease its severity by helping fill the state’s major reservoirs.
“The encouraging thing here, to use the oft-used expression, is that the storm door is open again,” said Jan Null, a meteorologist at Golden Gate Weather Services in Saratoga. “We aren’t seeing the blocking pattern that kept things dry in February.”
The National Weather Service issued a hazardous weather outlook from Sonoma to Monterey County, and said winds in the region could reach 30 mph at lower elevations and 50 mph in the mountains. Cobb and Middletown are under a flash flood warning.
If the storm system delivers as expected, it will be the wettest one in two months, since heavy rains driven by strong El Niño conditions in the Pacific Ocean lashed Northern California in early and mid-January.
The first big storm will appear today, peaking overnight into early Sunday morning. Then a second, somewhat weaker storm is forecast to follow on Sunday, tapering off Monday morning. Forecasters at Accuweather expect the system to dump 1.5 inches of rain on Lakeport and 1.67 on Cobb Saturday, followed by close to another inch Sunday.
Chances of rain persist next week, although there may be a day or two of dry weather. The long-range models show another series of storms possible the following weekend, bringing at least an inch of rain to Lakeport on Friday. Accuweather predicts the storm to begin Thursday for Cobb and other areas of higher elevation.
Today’s storm is being billed as an “atmospheric river.” Such fast-moving storms, often called “Pineapple Express” storms when they originate from Hawaii, are driven by high winds and carry vast amounts of water.
In a typical year, as few as half a dozen atmospheric rivers can deliver 50 percent of Northern California’s annual rainfall, said Marty Ralph, director of the Center for Western Weather and Water Extremes at UC San Diego.
On average, such storms carry 20 times the water as the Mississippi River at its terminus with the Gulf of Mexico, he said. The storm today will be a modest atmospheric river, about 300 miles wide as it hits the California coastline — enough to bring significant rain but not a catastrophic event that could cause major flooding.
“A single storm can’t end the drought, but it can help substantially,” he said.
There can be no doubt that California desperately needs the rain.
After the driest four-year period in recorded state history, the strongest El Niño conditions ever measured in the Pacific Ocean buoyed hopes by November that soaking rains would end the drought. Those conditions — marked largely by warm water at the equator off South America — have peaked but are still there and are expected to remain through May. During strong El Niño years, California usually experiences wetter-than-normal weather.
Big storms in January provided a wet start and good skiing conditions in the Lake Tahoe area. But after a high-pressure ridge blocked storms in February, summerlike conditions caused the state to fall behind. On Thursday, the Sierra snowpack — a vital source of the state’s water — was 80 percent of the historic average for that date, down from 116 percent on Feb. 1.
Lakeport received a scant 0.46 of an inch of precipitation in February, far short of the normal — non El Niño — mark of 6.12.
That should all change this weekend. The wettest areas of the state will be north of Santa Rosa, near the watersheds of California’s largest reservoirs. The biggest, Shasta Lake, was 29 percent full on Dec. 3, and on Thursday was 61 percent full. The lake level has risen 86 feet in the last three months. But to fill to the crest of the dam, it must come up another 69 feet. Other major reservoirs were similar: Oroville was 53 percent full Thursday, Folsom was 62 percent and San Luis, near Los Banos, was 44 percent.
“The storms this weekend are certainly going to hit the big reservoirs,” said Null. “That’s the big plus. And if you look at the seven-to-10 day charts, the big bulls-eyes are in those northern watersheds.”
Officials with the State Water Resources Control Board have said they will meet in mid-April to decide whether to relax Gov. Jerry Brown’s emergency drought rules that since last June have required urban water users to cut water consumption by 25 percent on average statewide.
It’s too soon to say whether the state will have a “March Miracle” similar to 1991, when several years of dry winter weather were broken by deluges that month.
“Right now, it looks like March is getting off to a good start,” said Daniel Swain, a climate researcher at Stanford University. “We do still have really strong El Niño conditions in the Pacific. It’s plausible that March could end up being a very wet March.”
