California's Snowpack at Record Early-April Low; Sierra Snow Survey Finds Bare Ground

California's snowpack has plunged to record low levels for early spring, bringing more ominous news for the drought-stricken state's water supply.

A statewide snow survey Wednesday found that the water content of California's snowpack was only 5 percent of the April 1 average, by far the lowest reading on record for that date. The previous record lowest snowpack for the first day of April was 25 percent of average, in records dating to 1950.

Manual snow surveys are typically performed in the Sierra on April 1, around the time of year when Sierra snowpack reaches its peak after a succession of winter storms dump feet of snow in the mountains. Automated electronic sensors measure the snowpack in other mountain locations in California, and throughout the West.

This year, the manual measurement of the Sierra snowpack performed at Phillips Station, located about 90 miles east of Sacramento, was done on bare grass for the first time.

The average snow depth at Phillips Station  (elevation 6,800 feet) in early spring was 66.5 inches in records dating to 1941, according to the California Department of Water Resources.

"We're in a historic drought and that demands unprecedented action," California Gov. Jerry Brown said at a news conference Wednesday at Phillips Station during which he announced mandatory statewide water restrictions for the first time in state history.

(MORE: Mandatory Restrictions | Community Nearly Out)

Roughly one-third of California's drinking water comes from the Sierra snowpack, which after melting later in the spring and summer replenishes the state's reservoirs.

One way to look at the Sierra's massive snow deficit is to consider Tahoe City, California, along Lake Tahoe's north shore.

From Oct. 1, 2014 through March 31, 2015, only 19.5 inches of snow had fallen in Tahoe City. That's 143.1 inches below average for that period, or almost 12 feet less snow than average. 

In fact, in Tahoe City it did not snow at all in January, typically the second snowiest month, averaging 40.3 inches.

Just how much of a water deficit does this translate to?

That may sound like a lot of water locked up in what is claimed to be a paltry snowpack this spring.

However NASA's Airborne Snow Observatory estimated 58 billion gallons of water content in the snowpack at its early spring 2014 peak in the Tuolumne River Basin. That's 34 billion gallons less in the basin's snowpack compared to last spring.

And that's only for one California River Basin.

Despite the record low snowpack, reservoirs in California are actually running about 5 percent higher now than they did after last spring's snowpack had melted.

"This dichotomy is largely due to the higher water content of the relatively warm December and early February storms and the runoff reaching the reservoirs sooner rather than later," said Jan Null, a consulting meteorologist in the San Francisco Bay Area, in an internal email.

"The three largest California reservoirs, Shasta, Oroville and Trinity, saw the greatest increases."

These December and February storms deposited less snow, but more rain in higher elevations, which ran off into reservoirs instead of building the snowpack.

Unfortunately, with a paltry snowpack, and typically little rain and mountain snow left to fall before the summer dry season, reservoirs will have little snowmelt available to recharge.

Tahoe City typically picks up only 16.4 additional inches of snow from April through June. Downtown San Francisco averages only 2.32 inches of rain, or just under 10 percent of its annual average rainfall, from April through June.

(FORECASTS: Lake Tahoe | Bay Area | L.A.)

Incidentally, it's not just the Sierra snowpack that is in record low early April territory. 

According to the USDA/NRCS National Water and Climate Center, many locations in the Cascades of Washington and Oregon, Bitterroots of Idaho and Montana and Wasatch of Utah are either near or setting new record low snow-water equivalent values for early April.

These values are as low as 7 percent to 31 percent of average in the Cascades, and 34 percent to 56 percent of early April average in Utah's Wasatch.

Despite a somewhat wetter April pattern ahead, it's clear Californians will have to ramp up water conservation efforst and hope for a much wetter winter 2015-16 to begin putting a dent in this multi-year drought. 

MORE ON WEATHER.COM: California Drought Photos (April 2015)