The storm that pounded California this week, unleashing mudslides on the coast and blanketing the Sierra with several feet of snow, chipped away at the state’s slowly emerging drought. But California’s water woes still loom.
Hills and valleys across the state that a week ago reeled from a third or less of average seasonal rainfall now stand at only around 50% of average or so. More wet weather is expected in coming days, though water experts say the trajectory of a year that’s been as dry as any recent drought year won’t change unless a number of storms like this week’s follow.
“We’re so far in the hole that we need a few more of them to get back to average,” said Jeanine Jones, interstate resources manager for the California Department of Water Resources. “And we’re running out of calendar in terms of our wet season.”
The impressive amounts of rain and snow that fell in recent days were the result of the state’s first major atmospheric river this winter. The wet front, essentially a massive plume of airborne water, ranked as a 3 on the weather community’s new 1-to-5 scale of atmospheric river strength. The rating applies to the apex of the storm, which fell on the Central Coast.
The Big Sur region, as a result, saw among the state’s highest rainfall totals this week. Close to 16 inches fell in mountain spots over two days, according to the National Weather Service. South of the Esalen Institute, a chunk of Highway 1 on the coast was washed away. At least 20 homes near Salinas were damaged by a mudslide.
Marty Ralph, one of the creators of the atmospheric river scale and a climate researcher at UC San Diego’s Scripps Institution of Oceanography, said the Central Coast sees a storm of this severity only about once every couple of years.
A home sits atop a hillside scorched by last year’s River Fire as heavy rains caused mudslides and flooding near Salinas on Thursday.
Noah Berger / Associated PressHis research team flew 12 flights, starting in Hawaii, into the atmospheric river to track its progress, forecast its path and try to better understand the role such systems play in dictating California’s weather and water supplies. A handful of these fronts, each of which can produce as much rain as a hurricane, typically provide half of California’s annual precipitation.
The recent system, which originated over the north Pacific and was fed by moisture from the tropics, was different from other atmospheric rivers only because it came after such a prolonged dry period, Ralph said.
Before this front, California’s closely watched Northern Sierra Precipitation Index, which tracks rain in an area vital to the state’s largest reservoirs, had barely a third of the rainfall that normally falls by this point in the season, which started Oct. 1.
“Here we have one of the driest years on record in some places and then we end up with this big storm,” Ralph said. “It’s probably reasonable to say that for much of the Sierra, this is not going to get us back to normal, but it might get us halfway there.”
On Friday, the Northern Sierra Precipitation Index measured 51% of its historical average for the date.
Meanwhile, the snowpack in the Sierra and southern Cascades was 66% of what it normally is at this point in the season, according to state records. The storm was responsible for a lot of that.
More than 7 feet of snow fell in the Kirkwood area south of Lake Tahoe this week, the weather service reported. Alpine Meadows ski resort on the northwest shore of Lake Tahoe saw 6½ feet of snow. The east side of the Sierra saw so much snow that U.S. Route 395 was shut down for more than 100 miles between Mammoth Lakes and the California-Nevada state line.
California has seen a handful of atmospheric rivers this year. Most, however, have been small or were the remnants of systems in Oregon and Washington that touched only the northernmost parts of the state.
Another atmospheric river is forecast to make landfall along the California-Oregon border late Saturday. It’s projected to be a 2 on the severity scale. The system is expected to weaken significantly before it moves into the Bay Area on Sunday night.
Typically, Northern California sees about 15 atmospheric rivers during the wet season, according to Ralph, with several as strong as this week’s storm. This year, however, has been atypical.
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With the wet season generally wrapping up in March, the Scripps Institution estimates the odds of average precipitation this water year, which goes through Sept. 30, at less than 25% for most of the state. The odds of getting 75% of average precipitation are less than 50% for much of the state.
Making matters worse, this rain year follows a dry year last year. That’s put a squeeze on California’s reservoirs, which generally hold enough water to go one dry year without impacts but begin to empty if a wet year doesn’t follow.
On Thursday, Shasta Lake, California’s largest reservoir, had 69% of the water it normally holds at this point in the season. Lake Oroville, the second largest reservoir, had 54% of its historical average. The 154 largest reservoirs cumulatively contained about 76% of their average water.
“We don’t have a crystal ball about what the wet season, which is rapidly growing short, will look like,” said Jones of the state Department of Water Resources. “But we’re now two-thirds through our normally wettest three months. ... The real question is what can we expect in this (remaining) period.”
Kurtis Alexander is a San Francisco Chronicle staff writer. Email: kalexander@sfchronicle.com Twitter: @kurtisalexander
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