A series of powerful Pacific storms is battering the western United States this week, unleashing days of heavy snow and rain across California.
Forecasters said the back-to-back systems could bring strong winds, dangerous surf, potential flooding and white-out conditions in some areas, with snow accumulations in the higher elevations reaching up to eight feet by the middle of the week.
These conveyor-belt storms arrive after a long stretch of dry and warm weather across the state. While the snow and rain could create hazardous travel conditions, Bob Oravec, a meteorologist at the Weather Prediction Center, said the precipitation is a welcome boost to California’s water supply.
“Over the past month or two they’ve been below average in precipitation,” he said. “But at the moment there’s no drought in California, so long term they’re doing well, and this will definitely help them out with their reservoirs and snow pack.”
The biggest impacts are expected in Northern California, particularly the northern Sierra Nevada and its foothills, the coastal ranges and parts of the northern Shasta region. In these areas forecasters said four to eight feet of snow could accumulate at higher elevations, while lower elevations may see up to a foot by Thursday. By Tuesday, nearly 33 inches of snow had accumulated at Donner Peak over 48 hours, with 27 inches of that having fallen within a 24-hour period.
Central California is also expected to see significant snowfall. The Hanford, Calif., office of the National Weather Service said that areas of the central and southern Sierra, including Yosemite, Kings Canyon and Sequoia National Parks, could receive up to seven feet at higher elevations. At the same time, the Reno office of the Weather Service said that northeastern California could see three to five feet along the Sierra crest, one to three feet in the Sierra valleys, including Tahoe, and up to six inches in the lower valleys.
Interstate 80, a main artery through the northern Sierra, was closed in both directions at times over the weekend.
Flooding around Los Angeles could become dangerous.
While snow will dominate over Central and Northern California, Mr. Oravec said wintry conditions could extend farther south.
“It’s not going to be a tremendous amount of snow,” he said. “But the range of mountains that are north of Los Angeles, some snow totals there could reach six to 12 inches above 4500 feet, but rain is going to be the primary thing for Southern California.”
Mr. Oravec added that Tuesday was expected to be the most impactful day for rainfall in Southern California, with showers and thunderstorms spreading south from the northern and central regions.
“Then after that there’s lighter precipitation into Friday when there a little bit of a break into the weekend, before maybe some more rain moves in early next week,” he said.
The Weather Prediction Center issued its lowest warning level for the risk of flash floods, a 1 on a 4-point scale, for the Central and Southern California coast through Wednesday. Forecasters said at least an inch of rain is likely, and the recent rainfall has left soils and burn scar areas particularly vulnerable to runoff, putting urban areas at higher risk for flash floods.
In Los Angeles county, evacuation warnings were in effect for areas around the burn scars left by recent fires, including the Canyon, Bethany, Eaton, Palisades, Kenneth, Sunset, Lidia, Hurst, Franklin and Bridge fires, with officials urging residents to be ready to evacuate if an order is issued.
The first round of storms, which began on Sunday, initially brought snow above 5,000 feet across Northern and Central California. Mr. Oravec said that system had moved into Southern California early on Tuesday. At the same time, a stronger storm was expected to move into the state, bringing snow to lower elevations and delivering additional heavy snowfall across the Sierra from Tuesday into Wednesday.
“Then another one comes in on Thursday,” he said. “And maybe another one again for the weekend.” Mr. Oravec added that the weekend storm could produce yet another round of heavy snowfall.
Forecasters said snow could fall at a rate of one to two inches per hour in many areas, with heavier bursts possible in parts of the central and southern Sierra Nevada. Other mountain ranges, including the Transverse Ranges, may also see heavy snow at higher elevations.
Strong winds are expected to be an added hazard. Forecasters said gusts over 100 miles an hour were expected along ridge tops, and valleys could experience gusts up to 45 m.p.h. Combined with heavy snowfall, near-zero visibility is expected at times, especially in the Sierra Nevada.
Winter storm warnings have been in effect since Sunday, covering a broad swath from southwest Oregon to parts of Southern California through late Thursday. The National Weather Service warned of “dangerous to near impossible travel conditions” in some areas.
Nazaneen Ghaffar is a Times reporter on the Weather team.
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