Drought May Reach Epic Proportions : Weather: Dry spell is expected to last through 1991. Northern Sierra snow season has been third driest in 70 years.

Despite rain this week in the south and extreme cold last month in the north, California’s drought is now all but certain to persist through 1991 and sits on the brink of becoming an epic event in the state’s history.

Nature’s tendency to follow patterns made the dry spell likely to break this winter, the fifth in the longest drought since the 1930s. Instead, the opening months of the snow season have been the third driest in 70 years in the northern Sierra Nevada, the main source of water for Southern California cities and Central Valley farms.

“The water supply picture in California is grim,” said Duane Georgeson, assistant general manager of the Metropolitan Water District of Southern California.

Water engineers stress that a solid month of heavy snow and rain could revise the picture--as occurred in March, 1989--but the odds against that are long. Typically, 40% of the winter’s snow and rain falls before Jan. 1. By January, precipitation was only 10% of what falls in an average winter.

The disappointing early winter means that even heavy snowfalls in January and February would leave California’s major reservoirs critically low. If the rest of winter is merely typical, state officials say California will be forced to endure this summer the most severe water-use rules most residents have seen in their lifetimes.

“It easily has that potential,” Georgeson said. The water district board will decide Tuesday whether to order its most severe water rationing ever, a 17% cutback to the Southern California cities it serves.

Before this drought, the last water scare in California came in 1977, the driest year in the state’s record books. Cities all over Southern California ordered water rationing to cut use by 10%, and the northern part of the state was hit even harder. Since 1977, the state has added 9 million thirsty, lawn-watering, toilet-flushing people.

For only the second time, the state is planning to cut its delivery of water to cities, mostly in Southern California. The proposed 15% cut is even bigger than the 10% cut imposed in 1977. Water for farms would be reduced by 65% from what growers typically receive. The trouble facing California is most evident at Oroville Dam, the biggest lake in the State Water Project. Oroville began the year holding less water than it did at the end of 1977.

“This is the lowest Oroville has ever been at this time of year,” said Bill Helms, a Department of Water Resources official.

State crews that measured the snowpack this week on mountains that feed the Feather River, the main source of Oroville water, discovered the extent of the continuing drought. Because the snow is shallow and unusually dry, it contains only about a third of the water usually found in snow in the Feather River basin in early January.

For example, at a measuring station on Lassen Peak, the crew found the snow 18 inches deep, but unusually low in moisture. A column of snow melted down would yield only 4.9 inches of water, compared to an average for January on Lassen Peak of 31 inches of water. At this time last year, the snow at the same spot held 16 inches of water.

Part of the problem, according to state water officials, was the crop-killing cold that enveloped Northern California last month. It brought only a dusting of snow, and it was too dry to contribute much runoff into mountain streams, which in turn fill Oroville and the other big reservoirs that allow most Californians to pretend they don’t live in a natural desert.

The cold air mass originated over land, in the Arctic, so the clouds that accompanied the cold carried little moisture. The storm systems that typically drench California in winter originate over the ocean--the central Pacific or Gulf of Alaska--where they pick up copious amounts of water vapor.

Also, a foot of snow this year will produce less spring runoff than last year because the soil in forests and canyons is itself bone dry after four long drought summers. The first snowmelt is going to soak into the ground rather than run off into streams.

Despite the bleak picture, weather watchers in the state Department of Water Resources said the drought came close to being flooded into a memory by the autumn storms that inundated cities in the Pacific Northwest. The storms came off the Pacific loaded with moisture, but were nudged to the north by winds off the ocean.

“We just missed getting hammered,” said Dale Heggli, a meteorologist with the state Department of Water Resources.

For the next 10 days at least, the storm situation is no better. Storms are coming to life over the Pacific, but the moisture is likely to fall either too far north or south to reach California’s dams, Heggli said.

If the water falls in the south, it would do little to ease the pain of the upcoming summer in the Los Angeles area, but it could help with the extreme shortage along the central coast from Santa Barbara to Monterey--an area that does not get any water from state dams. Before this week’s storm, Santa Barbara had received only 3% of its usual rainfall since Oct. 1 and had ordered a crash water saving program.

BARELY DAMP: Two days of rain have scarcely wet the edges of the city’s Herculean drainage system. B1

STORM DEPARTS: The storm that dumped rain on the Southland for two days finally moved off to the east. B3