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A powerful “atmospheric river” storm is expected to pummel Northern California starting Tuesday night and deliver heavy rain, gusty winds, downed trees, power outages and rough driving conditions Wednesday and Thursday.

“It is a classic Pineapple Express,” said Bill Patzert, a research scientist and oceanographer who retired last year from NASA’s Jet Propulsion Laboratory in Pasadena. “It’s coming from deep in the tropics south of Hawaii aiming right at the West Coast.”

This 3-hour precipitation loop off the latest NAM shows the expected timing of the rain from the next storm. Actual rain amounts may be higher in the coastal hills than what the NAM is forecasting. #cawx pic.twitter.com/8ZtP6PMfy5 — NWS Bay Area (@NWSBayArea) February 12, 2019

The storm should bring up to 5 feet of new snow in the Sierra Nevada, forecasters said. The National Weather Service announced flash-flood and high-wind warnings for the Bay Area, along with Santa Cruz and Monterey counties, from 10 p.m. Tuesday to 10 p.m. Thursday. And fears of mudslides prompted Caltrans on Monday to close a section of Highway 1, south of Big Sur, in both directions starting at 5 p.m. Tuesday.

In the Bay Area, the first big push of rain is forecast to arrive over the North Bay late Tuesday and spread inland Wednesday.

“Rain will spread over the area early Wednesday morning and impact the morning commute quite a bit,” said Spencer Tangen, a meteorologist with the weather service in Monterey. “Rain may be heavy at times as the atmospheric river moves onto land.”

Late last week, meteorologists and scientists studying computer models included the potential for this atmospheric river storm, which at the time was projected to be centered over Central or Southern California.

But over the weekend the forecast shifted, and the storm is now expected to have a greater impact in the Bay Area and Northern California, they say.

This potent storm is the result of a cold front moving down from the Pacific Northwest, combining with a plume of subtropical moisture moving in from Hawaii, according to the weather service.

GOES-17 shows two troughs- one off the Pac NW coast and one near Hawaii. These will phase (combine) on Tuesday. This will cause an #AtmosphericRiver with a tropical tap to take aim at California on Wednesday. #CAwx #CAstorm pic.twitter.com/WQMwUlUfHj — NWS Bay Area (@NWSBayArea) February 11, 2019

In the Bay Area, storm totals from Tuesday night through Thursday morning are forecast to range from 2 to 3 inches in the North Bay, 1 to 2 inches along the Peninsula, East Bay and South Bay and 4 to 6 inches along the coastal mountains, with some mountain areas receiving 8 inches.

“There is still some uncertainty with how much rain,” will fall and how long it will last, Tangen said.

Sustained winds of 30 to 40 mph are expected Wednesday with gusts of 60 to 70 mph in the hills.

“Given the saturated soils and expected rainfall, trees will likely come down,” the weather service wrote in its Monday forecast.

Unlike last week’s storms, this week’s won’t bring snow to Bay Area peaks. Forecast lows overnight are expected to remain in the 40s with daytime highs in the 50s.

Atmospheric rivers are a particularly moisture-heavy, intense type of storm. 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 providing up to 50 percent of the annual water supply in most years. They also can cause damage and flooding.

Patzert said as of Monday afternoon it looked as if the storm will cause some localized flooding and snow blizzards in the Sierra, but that overall it will benefit California’s water supply, particularly by boosting groundwater tables still low in some areas after the 2012-16 drought.

“It could be the most intense storm so far of this winter,” he said. “There’s always minor damage, but the bottom line here is water, and this is good for the water supply.”

Wednesday’s storm is expected to rank as a 3 on a new scale of 1 to 5 that scientists at Scripps Institution of Oceanography and other research centers developed recently, Jay Cordeira, a meteorology professor at Plymouth State University in New Hampshire, said on Twitter.

Meteorologists still are watching the trajectory of the storm to forecast where the heaviest rains are expected.

“There will be intense downpours in the coastal mountain ranges,” said Andrea O’Neill, a meteorologist and oceanographer with the U.S. Geological Survey in Santa Cruz. “We already have saturated soils, so that becomes a hazard for streams and flooding and landslides.”

“The potential is there for local impacts to be extreme,” she added. “But it depends on where it plays out and where it makes landfall.”

Caltrans announced Monday it will close Highway 1 south of Big Sur beginning at 5 p.m.Tuesday in landslide-prone areas. The closures are at Mud Creek, near Ragged Point, the scene of a massive landslide in May 2017 in which millions of tons of earth buried the road 9 miles north of the Monterey-San Luis Obispo county line. The second closure is at Paul’s Slide, about 13 miles north of Mud Creek near Lucia.

New scale to rank ‘atmospheric rivers’ like hurricanes – Read the article

Although small-stream flooding is expected in some places, major rivers are not expected to flood, according to the weather service. But local agencies are watching closely.

“That kind of intense rainfall can cause localized flooding, but we’re not expecting Anderson to fill or anything like that,” said Marty Grimes, a spokesman for the Santa Clara Valley Water District, referring to Anderson Reservoir near Morgan Hill, the largest of 10 district reservoirs. “Anderson has plenty of room in it.”

On Monday, Anderson Reservoir was 37 percent full. The reservoir filled in 2017 during heavy storms and its releases contributed to $100 million in flood damage to downtown San Jose. The water district has been letting water out since last week to keep Anderson’s level lower as more storms roll in.

Matt Startsev, 13, of Danville, bikes to the summit of Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)

Lincoln Feinstein, 6, of Los Gatos, eats a snowball and walks to school with his mother, Kourtney Feinstein, as snow covers the Santa Cruz Mountains along Summit Road on Tuesday, Feb. 5, 2019, in Los Gatos, Calif. (Jim Gensheimer/Special to Bay Area News Group)

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Doug Dahn, 18, Clarke Clemmons, 17, and Harrison Pavel, 18, of Danville, from left, carry surfboards as they hike to the summit of Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)



Mark Armstrong, of San Ramon, takes in the view from the observatory after hiking to the summit of Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. It was (Jane Tyska/Bay Area News Group)

Sue Rohlicek, front, and Gayle Lightfoot, both of Pleasant Hill, hike to the summit of Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)

Snow hangs onto grape vines Regale Winery as snow covers the Santa Cruz Mountains along Summit Road on Tuesday, Feb. 5, 2019, in Los Gatos, Calif. (Jim Gensheimer/Special to Bay Area News Group)



Enzo Ingwaldson, 7, of Danville, plays in the snow with family members on Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)

A snowy view of the Morgan Territory is seen from near the summit of Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)

Mark Sinclair shovels a path on the summit of Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)



A tree is covered with snow near the summit of Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)

Santa Cruz resident Josh Stiles has a snowball fight with his Hannah Stiles, 6, during a visit to Summit Rd in Los Gatos where a rare snowfall blanketed the Santa Cruz mountains. (Photograph by George Sakkestad)

A tree is covered with snow near the summit of Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)



Natalie Schmidt walks with her dogs, Olivia, at left, and Mitzi, at Summit Tree Farm as snow covers the Santa Cruz Mountains along Summit Road on Tuesday, Feb. 5, 2019, in Los Gatos, Calif. (Jim Gensheimer/Special to Bay Area News Group)

Trees are covered in snow at the summit of Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)

Gayle Lightfoot, left, and Sue Rohlicek, both of Pleasant Hill, take in the view as they hike to the summit of Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)



A sign is covered with snow on the summit of Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)

Jay Cassianni, of Berkeley, skis down the road from the summit of Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)

David and Renee Partridge, and their dog Margie, 13, of Walnut Creek, hike down from the summit of Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)



A view of the snow-covered summit of Mount Diablo is seen in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)

Sammy Baeza hurls fresh snowballs on Quimby Road in San Jose, Calif., Tuesday, Feb. 5, 2019. However, folks headed to Mount Hamilton were turned back at Joseph D. Grant County Park where the road was closed due to icy conditions. (Karl Mondon/Bay Area News Group)

SAN JOSE, CA - FEB. 5: Cactus growing on Quimby Road in San Jose, Calif., were probably a bit surprised this morning to find themselves covered in snow, Tuesday, Feb. 5, 2019. (Karl Mondon/Bay Area News Group)



SAN JOSE, CA - FEB. 5: A cyclist makes his way through the snowy hills on Quimby Road in San Jose, Calif., Tuesday, Feb. 5, 2019. However, the road to Mount Hamilton was closed due to icy conditions. (Karl Mondon/Bay Area News Group)

Enzo Ingwaldson, 7, of Danville, makes a snowball on Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)

A light covering of snow blankets parts of Mount Diablo seen from Walnut Creek, Calif., on Tuesday, Feb. 5, 2019. (Anda Chu/Bay Area News Group)



Amore Ingwaldson, 11,right, throws a snowball at her sister Zoe,10, of Danville, on Mount Diablo in unincorporated Contra Costa County on Tuesday, Feb. 5, 2019. (Jane Tyska/Bay Area News Group)

Photos from last week’s storms

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One thing is clear now: 2019 will not be a drought year. With recent storms, seasonal rainfall totals in most Northern California cities are close to or above their historical averages for this time of year, including San Francisco (13.72 inches, 92 percent of average), Oakland (10.84 inches or 87 percent), and San Jose (9.27 inches, 100 percent.)

On Monday, the Sierra Nevada snowpack measured 129 percent of historical average for this time of year.

More snow is on the way. Jim Wallmann, a meteorologist with the weather service in Reno, said he expects the storm to dump at least 3 feet of new snow in the Sierra at elevations higher than 3,000 feet. Some forecasts called for 5 feet at the highest mountain passes.

“Unlike the fluff this weekend, it’s going to be a wet, heavy Sierra cement type snow,” Wallmann said.