The Washington PostDemocracy Dies in Darkness

New winter storm could push California’s snowpack to record high

Reservoirs and rivers are also full as this round of rain, snow and wind arrives Monday night

The next storm targeting California was off British Columbia on Monday morning. (RAMMB/CIRA)
5 min

Here we go again. After a several-day break in the rain, snow and wind across California and the West Coast, another intense storm system is poised to slam into the region late Monday night into Tuesday. Heavy snow in the high terrain will make for difficult travel, while heavy rain in coastal, valley and foothill regions could cause flooding. Strong winds could trigger downed trees and power outages, particularly in the northern and central parts of the state.

In the mountains, the heavy snow will fall on top of already historic amounts.

Ahead of this storm, the amount of water stored in the state’s snowpack had approached or surpassed records in two of three regions. The southern Sierra blew past its previous record in late February and is running 284 percent of the annual normal as of March 27. After this storm hits, the state average could climb to a record high.

Winter storm warnings are in effect for the Sierra Nevada and much of Northern California into parts of Oregon. Generally, 2 to 3 feet is expected in the higher elevations from this storm, with some spots topping 4 feet. While snow levels will initially be around 7,000 feet, they will fall as low as 500 to 2,500 feet as a cold front passes Tuesday.

In the lowlands from southern Oregon to Southern California, several inches of rain are forecast. “The heaviest rainfall is expected Tuesday along coastal Central California,” the National Weather Service wrote Monday.

As the first part of the storm arrives, winds will also roar. Wind advisories are in effect for gusts around 50 mph in the San Francisco Bay Area, with even higher readings probable in the coastal ranges. The storm comes just one week after a bomb cyclone unleashed gusts up to 80 mph in the Bay Area, toppling trees and power lines. At least five people died as a result of trees falling on vehicles.

The storm set up

A storm embedded within a dip in the jet stream, sweeping down from the polar regions, has its eyes on the West Coast. On Monday, it was ominously swirling offshore Canada’s British Columbia while dropping southward. It will intensify somewhat and then remain quite strong into Tuesday as it focuses its fury on Northern California.

Precipitation will pick up Monday night in the north, reaching its maximum intensity in the Bay Area and central parts of the state Tuesday into Tuesday night, then easing some as it heads to the Southland through Wednesday.

The storm ultimately will rejoin the mid-latitude flow and finally scoots across the country late in the week. As it does, another outbreak of severe weather is possible in the central United States on Thursday and Friday.

Historic snow depths to increase

The snowy side of this storm will get underway Monday night in the Klamath Mountains of Northern California and adjacent parts of the Cascade chain in Oregon. Heavy snow then rolls southward through the Sierra through Tuesday. The heaviest snowfall will last about 10 hours, falling at a rapid clip.

Snowfall rates of 3 inches an hour or more are likely in the heaviest bursts Tuesday, leading to dangerous travel and probably some road closures.

New snow totals in the Sierra should commonly reach 2 to 4 feet. Some locations in Oregon and southern Washington could also see as much as 1 to 2 feet of snow by Thursday.

At the Central Sierra Snow Lab, the seasonal total was 692 inches after the most recent storm ended. It has seen its second-highest snowfall on record, behind 812 inches in 1951-52.

It’s a similar story up and down the Sierra, with ski areas posting record-challenging amounts. Palisades Tahoe, which announced that skiing will continue through July 4, has recorded 678 inches, and Mammoth Mountain is 1 inch off its record with 667 inches at the main lodge, and totals past 800 inches at the summit.

The Los Angeles Times reported that “average snow-water equivalent across the state was 58.1 inches, or nearly 5 feet, of water stored in the snowpack.”

Heavy rain and flood potential

The Weather Service’s Weather Prediction Center has declared a Level 2 of 4 risk for excessive rainfall for much of coastal California, running from near San Francisco to around Santa Barbara. A Level 1 of 4 risk also covers the Central Valley.

“This rainfall event is not expected to be as intense as the atmospheric rivers impacting the state in recent weeks,” the center wrote early Monday, but it added that previous heavy rains and high water levels increase the possibility of flooding.

The Bay Area and more mountainous terrain to its north (below snow levels) are likely to see the heaviest rain. In San Francisco, about 1 to 2 inches is forecast. North of the bay, more widespread totals of 2 to 3 inches are expected.

Across the central and northern part of the state, the heaviest rain should focus during the first half of Tuesday. Given saturated soils, any heavier rainfall could lead to at least localized flooding.

Almost all of California’s major reservoirs are now filled near or above historical averages, which is a stark turnaround from late last year, when many were as low as seen in recent times. Minor flooding on the Merced and San Joaquin rivers in Central California is forecast to persist amid the wet weather.

Winds could cause some problems, too

“Complicating the impacts of this storm will be strong gusty winds,” wrote the Weather Service office serving the Bay Area in a morning discussion. “Saturated soils plus winds makes it even easier for downed trees and power outages to occur.”

The main thrust of strong winds is forecast during the first part of the event, between Monday night and Tuesday afternoon.

Jason Samenow contributed to this report.