Swelling Sierra Nevada snowpack offers no reprieve for Sonoma County drought

The Mount Rose ski area, at 8,900 feet in the Sierra Nevada near Lake Tahoe, had 116 inches of snow Tuesday, with almost 3 feet freshly fallen since the day before Christmas.

The UC Berkeley Central California Snow Lab at Donner Summit on Tuesday morning reported more than 8 inches of snow in the previous 24 hours, bringing the total for December to 202 inches, the third snowiest month on record since 1970.

“It took us 40 minutes to get from the front door of the lab to where the measurement is completed 50 yards away,” lab researchers said in a tweet.

The California snowpack, which provides a third of the state’s water supply, was at 159% of normal for Tuesday’s date, the Department of Water Resources reported.

But if you think the heavy white blanket over the 400-mile mountain range will help ease the North Bay’s drought — think again.

“We don’t see that water in our area,” said Jay Jasperse, chief engineer and director of groundwater management at Sonoma Water, the North Bay’s dominant drinking water supplier.

Water for Sonoma, Mendocino and Marin counties comes from rainfall in the Russian and Eel River watersheds filling the region’s two major reservoirs: Lake Sonoma west of Healdsburg and Lake Mendocino at Ukiah.

Snow, like the white stuff this week on Pine Flat Road and Cobb Mountain in the Mayacamas Mountains, has only a “minor impact” on the Russian River system, Jasperse said.

“It just doesn’t linger,” he said.

In the higher-altitude Sierra and Cascade ranges, snow remains into the spring and summer, recharging California’s major reservoirs that feed into the state and federal water projects with aqueducts carrying water far to the south.

The big snowpack is “like a high-elevation reservoir that slowly releases water,” Jasperse said.

Heavenly Valley — with 76 inches of snow Tuesday — is at 8,800 feet near Lake Tahoe, nearly twice the elevation of 4,723-foot Cobb Mountain, where snow usually disappears within a day.

Despite a pair of heavy storms, called atmospheric rivers, in October and December, Lake Sonoma is about 55% full, compared with an 84% average for Tuesday’s date, and smaller Lake Mendocino is close to half full, compared with a 62% average.

Sonoma Water, which delivers Russian River water to more than 600,000 Sonoma and Marin county residents, is still urging conservation measures, noting the reservoirs hit historic lows this year.

“I know that’s a hard message (to understand),” Jasperse said. “You just have to look at the big picture. We still are filling the hole, so to speak” following two years of drought.

The recent heavy snows provide “a glimmer of hope” that has helped alleviate but not eliminate the statewide drought, a Department of Water Resources spokesman said Tuesday.

“More storms will be needed as we move through the winter season,” he said.

The federal government’s Drought Monitor last week showed nearly 70% of California, including the entire North Bay, in severe to extreme drought, the map’s second and third highest of four drought levels.

All of the state was in one of four levels, from moderate to exceptional drought.

You can reach Staff Writer Guy Kovner at 707-521-5457 or guy.kovner@pressdemocrat.com. On Twitter @guykovner.