After the driest beginning of any year in history, Northern Californians prepared Tuesday for a three-day rain spell that could provide some relief.

Weather forecasters predicted the approaching low pressure system would bring showers to the Bay Area and snow to the mountains by late Tuesday.

However, the National Weather Service said the stormy weather would likely only produce an inch of rain or less by the time skies cleared on Thursday.

In the Sierra, the stormy weather triggered a winter weather advisory with up to a foot of new snow forecasted for the higher elevations by the time the front move east.

While the pending storm will improve conditions somewhat, the snow so far has been dry and the water content of the snowpack is just 68 percent of normal, records show.

Much of that snow fell in December, and precipitation in the first two months of the year was barely over two inches, or about 13 percent of what is average.

"It's the third-driest January and February in Sacramento in 150 years and the driest in California since 1920," when statewide record-keeping began, meteorologist Peterson said.

The rains come a week after the latest Sierra snow survey found that January and February have been the driest on record.

Last week's monthly snow survey, anticipated by farmers and municipalities who depend on snowmelt to supplement water supplies, showed what everyone has known: despite a few good dumps the state hasn't received the kind of major storms needed to ease water managers' worries.

"It's disappointing, but not really a surprise," said Frank Gehrke, who as head of California's cooperative snow survey program takes manual measurements once a month near Echo Summit in El Dorado County to supplement electronic monitoring.

Gehrke measured 29 inches of snow with a water content of 13.4 inches. The dismal numbers still are twice as much as what was on the ground at this time last year, he said.

There is potentially good news coming by the middle of next week when the National Weather Service forecasts a sizeable storm that could bring more than two-feet of snow across the northern and southern Sierra and up to three-quarters of an inch of rain to the valley.

"The system we're tracking looks fairly potent," said meteorologist Drew Peterson. "It will really help the snowpack and help alleviate the dry start to the calendar year."

Historically about 15 percent of the state's annual precipitation falls in March. Gehrke measured the moisture content of the snowpack at 57 percent of average for the season that ends April 1.

California's Sierra Nevada snowpack provides about one-third of the water used in the state as it melts to fill reservoirs and rivers and replenish aquifers. Water is then delivered from the water-rich north through a system of state and federal canals that have turned arid southern deserts into thriving cities and rich farmland.

Southern California water users have been told to expect 40 percent of their allocation based on current measurements.