Hopes for much-needed moisture but fears of mudflows marked California as a Pacific storm headed toward the drought-dry state.

Rain was expected to begin falling Tuesday, although the timing of the heaviest downpours was variable, according to the National Weather Service.

Storm watches were posted for a large swath of the Sierra Nevada, where a huge amount of the state's water supply is normally stored as snowpack. Significant accumulations were predicted but not enough to be a drought buster.

Any delight over the prospect of beneficial precipitation was tempered by concerns about the threat of debris flows from the many areas of California where wildfires have burned away vegetation that would keep soil stable.

A weak storm Sunday was enough to block Pacific Coast Highway west of Malibu with a flow of mud from a section of the steep Santa Monica Mountains denuded by a 44-square-mile fire last year.

The muck was cleared but debris basins that overflowed were still full and will keep the highway from reopening anytime soon.

"We're going to have to wait until the next storm passes," said Patrick Chandler of the California Department of Transportation.

Residents placed sandbags to protect properties in foothill cities northeast of Los Angeles, where some communities below steep mountains have long lived with concrete barriers lining streets in hopes of keeping debris flows out of homes.

Glendora resident Cory Hansen piled sand bags around his home.

"Hundreds, hundreds of them," he told KABC-TV. "We don't know what's going to happen in the next few days."

Back-to-back storms are helping some cities in northwest California reach normal rainfall amounts for the year, or even better, but the reservoirs and Sierra snowpack that provide much of the state's water remain far short of what they should be, after three years of intense drought.

The state Department of Water Resources reported the Sierra snowpack, which counts most for the state's water supply, was at 24 percent of normal for this time of year.

Rain so far, at this early point in California's wet season, has yet to make much of an impact on the state's main reservoirs. Lake Shasta and Lake Oroville have less than 50 percent of their usual water level for the start of December, while Folsom Lake stands at 59 percent, said National Weather Service forecaster Eric Kurth.

"The good news is there's more storms on the way," Kurth said.