A trifecta of early winter storms that swept California with heavy rain and snow in the past two weeks put a promising dent in a severe drought entering its fourth year, but the water shortage remains far from over, water officials said on Tuesday.

Depleted reservoirs and the Sierra Nevada snowpack, which normally constitutes the state's largest natural store of fresh surface water, received a welcome boost from successive Pacific storms on Dec. 1-2, Dec. 11-12 and again on Monday and Tuesday.

But the reservoirs and the snowpack were still at levels well below average. Wetter-than-normal weather - on a magnitude of 150 percent of average - would have to continue through the winter to provide substantial drought relief, officials for the state Water Resources Department said.

"We're on the right track," department spokesman Doug Carlson said. "We have to wait and see what Mother Nature delivers and hope she's generous to us during the wet months, and by the end of February, we should know whether we're having a good year or a bad year."

He pointed to Lake Shasta in northern California, the state's largest reservoir, which was at 39 percent of its historic average level on Dec. 1 and has since risen to 52 percent. That's a big jump, "but we're still only halfway to average," Carlson said.

Likewise, the Sierra snowpack was measured on Tuesday at 48 percent of normal, up from 28 percent for the same date a year ago and 24 percent two weeks ago, he said.

In Southern California, which imports most of its water from northern California and out of state, the situation is complicated by a 15-year drought in the Colorado River watershed, said Bob Muir, spokesman for the Metropolitan Water District of Southern California.

The district expects to receive 10 percent of its contracted water allocation from northern California in the coming year, double the current level. Otherwise, the district will have to impose new restrictions on water it distributes to its member agencies, Muir said.

With showers dousing Southern California on Tuesday, areas stripped bare of vegetation by wildfires braced for a new round of mudslides. Flash flood warnings were issued in some places, but rain was generally less heavy than during the two previous storms.

Yet another storm, the season's fourth, was moving ashore in northern California late Wednesday and was expected to reach Southern California on Thursday, the National Weather Service said.