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After a few light sprinkles in recent weeks, Northern California is about to be pounded by a robust, find-your-flashlight-and-keep-an-eye-on-the-rising-creek winter storm. An “atmospheric river” is expected to soak most Bay Area cities Wednesday with 1 to 3 inches of rain and blanket the Sierra Nevada with a blizzard dumping 2 to 5 feet of snow.

The heaviest rains should arrive as part of a cold front Wednesday afternoon through Thursday morning, bringing wind gusts of 50 to 70 mph in the hills, the risk of small streams flooding, downed trees and possible power outages.

“Compared to previous storms we’ve had this winter, this is definitely going to be one of the more notable storms,” said Matt Mehle, a forecaster with the National Weather Service in Monterey. “It is going to bring heavy rain, really strong winds and high surf.”

By mid-day Tuesday the weather service issued a flash flood watch for streams and creeks from Big Sur to the North Bay during Wednesday afternoon and evening. “Urban and small stream flooding will become likely along with rapid rises on main-stem rivers,” the agency said in an alert.

Although they recommended that people in particularly low-lying areas near creeks put out sand bags to protect their property, forecasters said that major rivers are not expected to flood. The Russian River at Healdsburg in Sonoma County — one of the most flood-prone rivers in the Bay Area — is forecast to rise from 3 feet Tuesday to 14 feet by Friday, the National Weather Service estimated, but then will fall again over the weekend as the storms fade. Its flood stage is 23 feet.

Similarly, rivers like the Guadalupe and Coyote Creek in San Jose are expected to rise, but remain below their flood levels.

“We’re looking at the risk of some small, flashy creeks flooding. But we aren’t expecting any big flooding problems,” said Marty Grimes, a spokesman for the Santa Clara Valley Water District. “It will be windy though, so trees could fall and cause some obstructions.”

The storm could bring 6 to 10 inches of rain in the Santa Cruz Mountains and Big Sur by Friday morning. Most Bay Area cities will see 1 to 3 inches, which will help boost winter rainfall totals back to near 100 percent.

“On a statewide basis, from the Oregon border to San Diego, I think everybody is going to benefit from this,” said said Ryan Walbrun, a meteorologist with the National Weather Service in Monterey. “A lot of snow will be dropped in the Sierra. It’s a pretty big storm, there’s no doubt about it.”

Late Tuesday, the National Weather Service issued a blizzard warning for the Sierra Nevada on Wednesday and Thursday. The bulletin warned of “potentially life threatening conditions” above 7,000 feet in elevation, with winds up to 110 mph on ridge tops and high avalanche danger. It urged motorists to avoid mountain roads.

Atmospheric rivers are a particularly moisture-heavy, intense type of storm event. They can be 250 miles wide, 1,000 miles long and can carry 20 times as much water per second as the Mississippi River where it empties into the Gulf of Mexico.

Such storms are vital to the water supply of California and other Western states, with about a dozen significant ones providing between 25 and 50 percent of the annual water supply in most years.

“This is a very productive event. There are places in California that will get up to 10 inches of rain over the next week,” said Marty Ralph, director of the Center for Western Weather and Water Extremes at UC San Diego. “That could be 10 percent of the average annual precipitation for many parts of California.”

In years when there are more atmospheric rivers than average, serious flooding can occur. An atmospheric river storm last January caused major mudslides in Santa Barbara County over an area that had been burned the previous month in the Thomas Fire near Montecito. Those mudslides killed 21 people, injured 163 and destroyed 65 homes.

On the flip side, there can be droughts in years when there are fewer atmospheric rivers than normal, such as during the state’s 2011-2016 historic drought, when relentless ridges of high pressure air blocked many such storms from reaching California.

When the storms originate from Hawaii and tropical areas of the Pacific, they are called “Pineapple express” storms.

The storm Wednesday is not a Pineapple express, said Mehle. It is coming from about 200 miles north of Hawaii.

A weaker storm Tuesday dropped one-quarter to half an inch of rain across much of the Bay Area, with some locations seeing nearly an inch. As of 4:30 p.m., 24-hour rainfall totals included .87 inches in Kentfield, .68 inches in Gilroy, .50 inches in San Francisco and Oakland, .27 inches in Concord, .24 inches in Livermore and .23 inches in San Jose. The wettest area was Ben Lomond in the Santa Cruz Mountains, which received 2.36 inches in the 24-hour period ending at 8 p.m., according to the weather service.

FLASH FLOOD WATCH IN EFFECT FROM WED PM THROUGH LATE WED NIGHT.

Urban and small stream flooding will become likely along with rapid rises on main stem rivers. Small creeks and streams may rapidly rise near or above bankfull.

TAKE ACTION NOW TO PROTECT PROPERTY #sandbag #cawx pic.twitter.com/74cbuLwIYr — NWS Bay Area (@NWSBayArea) January 15, 2019

The rain is forecast to taper off by Friday. But before it’s over, snow levels will fall to as low as 4,000 feet on Thursday, meaning the highest Bay Area peaks could see a dusting. Some hail is also possible Thursday.

The storm system is expected to bring snow levels in the Sierra Nevada up to 100 percent of the historic average for this time of year. On Tuesday morning, snow levels were 84 percent of normal, following a sub-par November and December.

Although the weather service does issue roadway closures, Walbrun said he would be surprised if Interstate 80 and Highway 50 remain open at pass levels during the height of the storm Thursday. He advised travelers to avoid driving to Lake Tahoe or Reno during the storm.

“This is the type of storm that I would be stunned if there’s not prolonged closures on the interstate,” Walbrun said.

Active weather returns this week to the Sierra and Western Nevada. Expect major travel impacts Wednesday-Thursday. Blizzard conditions and road closures will be possible at high elevations. If you cannot delay travel over the passes, start making preparations now #CAwx #NVwx pic.twitter.com/vRuvYXx1b4 — NWS Reno (@NWSReno) January 14, 2019

After a slow start in November and December, a series of January storms has boosted rainfall totals across the Bay Area, though the region remains in a precipitation deficit for this time of year. Since the start of the rainfall season Oct. 1, San Francisco has received 7.76 inches of rain, or 71 percent of its historic average through Jan. 14. Oakland has received 6.74 inches, or 68 percent of normal; and San Jose has recorded 4.59 inches of rain, or 71 percent of normal.

But with soils saturated and creeks and rivers rising, reservoir levels should come up this week also, improving the summer water outlook.

“It’s definitely going to help,” said Mehle. “This week is going to be moving us in the right direction.”

Staff writer Jason Green contributed to this report.