Drought deja vu: California snowpack at 30 percent of normal

A couple watches the waves at Lands End in San Francisco, Calif. Monday, Jan. 29, 2018. Bay Area weather forecast suggests that little rain is in the near future and February to be the warmest on record. A couple watches the waves at Lands End in San Francisco, Calif. Monday, Jan. 29, 2018. Bay Area weather forecast suggests that little rain is in the near future and February to be the warmest on record. Photo: Mason Trinca / Special To The Chronicle Photo: Mason Trinca / Special To The Chronicle Image 1 of / 4 Caption Close Drought deja vu: California snowpack at 30 percent of normal 1 / 4 Back to Gallery

Yosemite’s Half Dome saw a picturesque dusting of snow this past week while skiers in Tahoe welcomed a shot of fresh powder. Yet California’s Sierra Nevada is plunging deeper into a warm, dry winter that shows little sign of a turnaround.

Mile-high mountainsides were low on snow Monday and alpine skies remained a stubborn summer blue. The forecast called for above-average temperatures and virtually no precipitation through at least the first 10 days of February — the third and final month of the state’s peak wet season.

When state water officials march into the high country Thursday to take their monthly measurements of snow, they’re going to find a deficit nearly as acute as what they found during the depths of the recent drought. At the start of the week, statewide snowpack averaged just 30 percent of normal for the date, not far from the 25 percent logged at the same time in 2015, a record-low year.

“It’s disappointingly dry,” said Doug Carlson, a spokesman for the California Department of Water Resources. “We’re just barely above that very bad year.”

State water officials say the situation is not as dire as 2015, because the drought-ending storms last winter helped refill rivers and reservoirs after five dry years. Nonetheless, the lack of snow has begun to trigger some concern.

The seasonal snowmelt in the Sierra, which accounts for about a third of California’s water supply, was projected earlier this month to come in short — 71 percent of average in the San Joaquin River watershed and 89 percent in the Sacramento River watershed. Those estimates are expected to slip further with this week’s snow measurements.

If the weather continues to be warm and dry through the first week or two of February, as forecasters expect, even less water will come from the mountain snow.

“Right now we have a snowpack that is very close to the all-time record low for this time of year,” said Daniel Swain, a climate scientist at UCLA who closely tracks California’s water supplies.

“Not only are we not adding to this dismal snowpack, but we’re detracting from it,” he said, noting that high temperatures may begin melting snow at lower elevations. “We’re going to be going in the wrong direction for the next couple of weeks.”

Come March, the chances of making up the snow deficit are greatly reduced. Half of California’s annual precipitation has historically fallen in December, January and February.

Climate experts say the dearth of snow is as much the product of heat as it is a lack of precipitation. While Sierra rainfall has been lower than average this winter, many of the storms would have produced more snow had temperatures been as cool as they’ve been in the past.

“In the last 10 or 15 years, the snowline had been marching up the mountains pretty quickly,” said Swain. “Unfortunately, that’s the reality. It’s one of the most obvious impacts of global warming.”

This winter, elevations of 5,500 to 6,000 feet, which were typically blanketed with snow just a decade ago, have been mostly dry. Only peaks and ridges above 10,000 feet have been consistently white.

The U.S. Drought Monitor, which considers a number of factors such as snow and rain to track nationwide water shortages, deemed 54 percent of California to be abnormally dry in its latest report. About 13 percent of the state, all in the south, was considered to be in a drought.

On Monday, California water officials announced that deliveries from the Sierra’s state-run reservoirs to cities and farms would be limited to 20 percent of the amount requested. That’s slightly more than what was expected to be doled out in December, but still a lackluster sum that reflects ongoing water concerns.

The State Water Project is one of California’s major suppliers, sending water to the East Bay and Silicon Valley. Its actions typically mirror those taken by local and federal water agencies. State officials said they’ll increase water allocations only if the winter outlook improves.

Sean de Guzman, an engineer for the state Department of Water Resources, said he’s not too worried yet. Storms are still possible in the back half of February as well as in March and April, he said, and all it takes to improve the water picture is a couple of major blasts.

He noted that supplies in California’s biggest reservoirs remain plump from last year, with Shasta Lake at 109 percent of average for the date and New Melones Lake near Angels Camp (Calaveras County) at 140 percent of average.

“Even if we were to have a really dry year with snowmelt and runoff, we’d be pretty OK,” de Guzman said.

The National Weather Service said dry conditions will persist across much of the state for at least the next week. Many areas will see above-average temperatures as well. On Monday, much of Southern California was experiencing record highs, with Long Beach Airport hitting 91 degrees and Los Angeles International Airport getting up to 89.

“It’s almost in the 90s here,” said Swain, who wore shorts to his UCLA office on Monday. “This would be considered a pretty hot day in July, much less January.”

Kurtis Alexander is a San Francisco Chronicle staff writer. Email: kalexander@sfchronicle.com Twitter: @kurtisalexander