3-YEAR FORECAST CALLS FOR DRY SPELL; LA NINO IS BACK WITH A VENGEANCE.

Byline: Robert Monroe Staff Writer

La Nina is gaining substantial momentum, possibly a harbinger that Southern California can expect two or three years of dry weather, experts said Wednesday.

Earlier forecasts cast doubt on whether the global weather phenomenon would return for a second year, but new infrared satellite images of the Pacific Ocean confirm: La Nina is back and getting stronger.

``She was in hibernation for a while, but she has definitely come out this fall and she is as strong as a year ago,'' said Bill Patzert, a scientist with the National Aeronautics and Space Administration's Jet Propulsion Laboratory in Pasadena.

``Everything is stronger than what we said in October. Everything is pumping up,'' he said.

The bad news is that Southern California can expect a cold but dry winter, with most storms dipping no farther south than Northern California, experts said. This happens at a time when Southern California is in the midst of a severe wildfire season.

Already in the rainy season, Los Angeles is on course for a drier-than-average calendar year, with just 9.52 inches of rain since January, compared with the average of 15.06 inches a year measured since 1877.

Still, that doesn't come close to the driest year on record, 4.85 inches in 1961, or the driest since a drought swept the whole state, 7.35 inches in 1990.

The National Weather Service anticipates no storms over the weekend to add to this year's totals. Meteorologist Jonathan Slemmer predicted winds from 15 to 25 mph and high temperatures rising from the mid 60s to the mid 70s by Saturday. Lows will be in the high 40s, he said.

New evidence of La Nina's re-emergence coincided with a meeting this week of a national panel on drought preparedness in Los Angeles. The National Drought Policy Commission was formed early in 1999 to help shape federal policy in dealing with droughts.

For Angelenos, however, the good news is that Los Angeles gets most of its water from the Sierras, where La Nina last year helped dump 1-1/2 times the normal amount of snow.

Los Angeles Department of Water and Power officials said that as long as enough snow falls in the Sierra Nevada range, they have no worries. Last year, Angelenos demanded 204 billion gallons of water. This year, the DWP estimates they'll demand 208 billion, the rise attributable to rising population.

``If we had two or three years of significantly less snowpack, then we'd start to worry about the years after that,'' said Fred Barker, a DWP water works engineer.

La Nina and its flip-side phenomenon, El Nino, are governed by temperatures of the Pacific Ocean along the equator. In La Nina years, cold water congregates in the eastern Pacific and warmer water in the west. In El Nino years, the cold and warm water masses swap places.

Patzert said that indicators of La Nina were obscured by distorted temperature readings over the summer, when the Northern Hemisphere gets the most sun and water at the ocean surface gets heated. The satellite probes to a depth of 650 feet to get its readings. Because of the summer distortions, scientists consider fall and winter readings more reliable.

Ants Leetma, director of the National Weather Service Climate Prediction Center in Washington, D.C., said La Nina will affect global climate for the next nine months, the time period which computer models can reliably predict.

Scientists are less certain about the year after that, but Leetma and Patzert said they foresee a repeat of the mid-1980s, in which two years of La Nina weather followed an intense El Nino in 1982 and 1983.

Reinforcing the possibility of a carry-over of dry weather into 2000 is the strength of the current La Nina in its second year, Patzert said. ``It has similarities to the mid-80s to the early 90s, when we were in a seven-year drought,'' Patzert said.

In addition, a much longer and larger-scale weather cycle observed only in the last 20 years is peaking, he said. Named the Pacific decadal oscillation in 1997, this phenomenon causes water temperature in the north and south Pacific to rise gradually over the course of a decade or more, pushing the jet stream south and generally warming California.

This gradual warming cycle has lasted 16 years, which means it began when the 1982-83 El Nino ended, he said.

``When that pattern locks in, it's usually good for a few years,'' Patzert said.

Patzert added that this year's pattern is nearly identical to last year's, when the snowpack in Northern California, the source of most local water, was extra heavy even though Southern California was dry.

Not all scientists agree.

Dan Cayan, director of the climate research division of the Scripps Institution of Oceanography in San Diego, said a natural backlash to La Nina could return conditions to normal.

``I think we may wipe the slate clean,'' he said. ``That doesn't mean it can't be dry but it means we aren't under the influence of that La Nina scenario.''

The data signaling the return of La Nina comes from the TOPEX/Poseidon satellite operated jointly by NASA and the French space agency CNES. The satellite measured over a 10-day period earlier this month that sea surface levels were three to nine inches below normal heights in the eastern Pacific Ocean. That indicates that the water is more dense and therefore colder than normal.

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Chart: Dry season