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California snowpack off to promising start, but drought concern remains

Cars slowly make their way as heavy snow falls on the Mt. Rose Highway near Reno, Nev., on Dec. 1, 2022. (Jason Bean/AP)

Winter is off to a running start in California, after a pair of December storms dropped several feet of mountain snow and soaking low-elevation rains across much of the state. Parts of the Sierra Nevada have recorded more than double the expected snowpack for the time of year, and another significant storm could be on the way this weekend.

However, officials are urging caution and conservation given the depth of the state’s water supply challenges. Longer range outlooks still point to a fourth consecutive drought year for the state.

Statewide snow water equivalent — or the amount of water contained in snowpack — is currently 175 percent of normal for the date. The Central Sierra Snow Lab, located at Donner Pass northwest of Lake Tahoe, is now sitting at 253 percent of its average.

Andrew Schwartz, lead research scientist at the lab, said that while these numbers are very good news, averages can be deceptive this early in the season.

He used a football analogy to put the December snow in context.

“We’ve scored a touchdown in the first quarter of the game, but we still have three quarters to go,” he said. “If we get to March and April and we’re still well above average for the time of year, then it’s time to celebrate.”

Water managers typically measure peak snowpack on April 1 to gauge the amount of water received during the heart of the wet season, after which snow is expected to melt and flow into streams and reservoirs.

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As of Dec. 5, statewide snowpack was 24 percent of the April 1 average, meaning that California is about a quarter of the way to an average snow year. But even that solid foundation is not guaranteed to last.

“That’s not a static number; we could still lose that if the storm cycle shuts off and we get into a warmer period,” Schwartz said.

Recent winters have featured dramatic twists and turns that ultimately landed on the dry side.

“Parts of California are seeing rain today, but forecasts for the rest of winter are still highly uncertain & highly variable,” the California Department of Water Resources tweeted on Monday. “Last year we saw a record-breaking October and December which gave way to the driest January through March period on record.”

Those wild swings are expected as the atmosphere warms, with stronger storms separated by longer and more severe dry spells — both intensified by climate change.

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For now, the storm door is expected to remain open. Multiple atmospheric rivers could make landfall over the West Coast in the next week, according to the Center for Western Weather and Water Extremes, with a substantial storm possible in California this weekend. The National Weather Service Climate Prediction Center is also forecasting a good chance of above normal precipitation through at least mid-month, particularly for Northern California.

But the state needs a well above average water year, or several wet years in a row, to replenish its reservoirs, which have been depleted by three years of extreme drought — the driest 3-year period on record in California. Schwartz said the Central Sierra Snow Lab would need 60 feet of snow this year to make up for what was lost during that time.

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Last week, the California Department of Water Resources announced that the State Water Project, which provides water to 27 million people and 750,000 acres of farmland, will again severely restrict water deliveries to just 5 percent of requested supplies in 2023. That number may increase if this winter turns out to be particularly wet, with a final allocation announced in May or June.

If dry conditions continue, more than 70 urban water agencies face potential shortages in the next 6 months, which officials believe can be remedied with increased conservation and other actions, according to a recent report.

“This early in California’s traditional wet season, water allocations are typically low due to uncertainty in hydrologic forecasting. But the degree to which hotter and drier conditions are reducing runoff into rivers, streams and reservoirs means we have to be prepared for all possible outcomes,” Department of Water Resources Director Karla Nemeth said in a statement last week.