Click photo to enlarge
Frank Gehrke, chief of snow surveys for the Department of Water Resources, checks the weight of the snowpack survey tube during the snow survey at Echo Summit Calif., Thursday, Feb. 28, 2013. The survey showed the snow pack to be 29 inches deep with a water content of 13.4 inches, which is 57 percent of normal for this site at this time of year.(AP Photo/Rich Pedroncelli)

After the driest January and February in the Northern Sierra since modern records were first kept in 1920, California's Sierra Nevada snowpack has dropped sharply to 66 percent of normal, state officials announced Thursday.

The snowpack, a key component of California's summer water supply for farms and cities, was at 93 percent of normal a month ago and 140 percent of normal on Jan. 1. The lack of significant rain and snow since New Year's Day is the result of a high-pressure ridge over the West Coast that has blocked storms from reaching California. And the dry weather is raising concerns among water officials and Central Valley farmers.

But the news isn't all bad: Because of heavier-than-normal rain and snowfall in November and December, many of the state's major reservoirs remain at or above normal levels.

"It's clearly not what we'd hoped for. But it's not as dire as it could be," said Frank Gehrke, chief of the California Cooperative Snow Surveys Program with the state Department of Water Resources.

On Thursday, Shasta Lake, the largest reservoir in California, was 79 percent full -- 107 percent of normal for this date.

Because of such storage, along with healthy water supplies in their own reservoirs and underground aquifers, no Bay Area water districts are predicting summer cutbacks or water rationing.


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"We were getting close to having one of the wettest years ever. It was on a good track, and then it flattened out," said Steve Ritchie, assistant general manager of the San Francisco Public Utilities Commission, which operates the Hetch Hetchy water system.

But, he said, "that's why we have reservoirs."

Nor is it time to start throwing around the D-word. Typically, water experts in California say there must be at least two years of substantially below-normal rainfall to qualify as a drought.

"From a water supply perspective, we're not in a drought," Gehrke said. "Clearly, the concern is that you can handle one or two dry years, but when they stack up, that's a problem."

Apart from the lack of snow in the Sierra in the past two months, rainfall in the Bay Area also slowed to a trickle in the first two months of the year.

January and February were the third driest since 1850 in San Francisco. San Jose had the driest January and February since 1874, when records were first kept. Even so, the yearly rainfall totals across the Bay Area remain respectable.

Boosted by soaking storms at the end of 2012, San Jose as of Thursday had 8 inches of rain since the rainfall year began last July 1, which is 71 percent of normal for this date. Oakland has had 11.8 inches, or 77 percent of normal. And Livermore has had 9.41 inches, or 80 percent of normal.

More sunny skies are forecast through the weekend. After that, there's a 30 to 50 percent chance of rain in the Bay Area early next week, probably on Tuesday and Wednesday.

"Nothing monstrous, but a quarter or half inch," said Jan Null, a former National Weather Service meteorologist who runs Golden Gate Weather Services in Saratoga.

That storm system also is expected to bring new snow to the Sierra.

Why did the rain and snow suddenly turn off in California in January and February?

Basic meteorology, said Null, who explained that as storm systems come barreling out of the Pacific, they move east with the jet stream.

Two months ago, however, a ridge of high pressure built up along the West Coast. So rather than dumping rain and snow over California, storms have been hitting the high-pressure ridge and getting pushed northward over Canada. Then they've been descending over low-pressure areas in the Midwest, blanketing that region with snow.

The National Weather Service's long-term projections out to 90 days don't show the high-pressure system going away.

However, "even if we don't get another drop of rain this year, it's not as disastrous as some of the years we've seen historically," Null said. "And we can still hold out hope for a March miracle."

Customers in the Peninsula and San Francisco who receive Hetch Hetchy water are in good shape because Hetch Hetchy Reservoir in Yosemite National Park is 70 percent full, and Crystal Springs Reservoir, near Interstate 280, is 94 percent full.

In Santa Clara County, no summer water cutbacks are expected, said Marty Grimes, a spokesman for the Santa Clara Valley Water District. That's due largely to the fact that the vast underground aquifers where the district stores water are above normal levels. They are on pace to hold about 326,000 acre feet by the end of 2013 -- an amount equal to all the water used by the county's 1.8 million people in a year.

Meanwhile, the district has another year's supply -- 308,000 acre-feet -- stored underground near Bakersfield at the Semitropic Water Storage District.

In the East Bay, the story is similar.

"We're looking OK," said Jennifer Allen, a spokeswoman for the Contra Costa Water District. "We're comfortable we're going to be able to meet our customer demand."

Part of the reason is that Contra Costa has more storage this year. Last summer, construction crews finished adding 34 feet to the height to Los Vaqueros Dam, a $120 million project that increased the reservoir capacity by 60 percent.

No summer cutbacks are expected at the East Bay Municipal Utility District, which serves 1.3 million customers in Alameda and Contra Costa counties. The district's main storage area, Pardee Reservoir in Calaveras County, was 84 percent full on Thursday.

"We came into the year with more water than we normally have, and we kept the early rainfall in the reservoirs, rather than letting a lot of it out to make space for future storms," said East Bay MUD spokesman Charles Hardy. "The strategy really paid off."

Paul Rogers covers resources and environmental issues. Contact him at 408-920-5045. Follow him at Twitter.com/paulrogerssjmn.