DRIER WINTER AHEAD, FORECASTERS PREDICT; PACIFIC CHILL SIGNALS RETURN OF LA NINA.

Byline: Alex Roth Daily News Staff Writer

The nation's top weather forecasters concluded Thursday that a La Nina winter is likely, heralding less rain for Southern California than usual - an ominous sign for the coming wildfire season.

At a specially called meeting in Boulder, Colo., meteorologists and climatologists charted the arrival of this global weather phenomenon, signaled by the formation of a pool of cold Pacific water larger than California itself.

This cooling of the ocean around the equator affects the jet stream, changing weather worldwide. In Southern California, it brings drier-than-usual winters rather than El Nino's wetter-than-normal weather.

Los Angeles already faces the prospect of brush fires, firefighters say, because of the large amount of brush and grass, grown lush with El Nino rains.

Among the unknowns is exactly how dry this winter will be and whether the La Nina phenomenon will have any effect on the hot, fire-stoking Santa Ana winds.

In the past eight La Nina years since 1950, Los Angeles received 13 percent less rainfall on average than during a normal year.

Still, forecasters hesitate to make any predictions at this early stage.

``The most likely scenario is that it will be slightly drier than normal,'' said Klaus Weickmann, research meteorologist with the Climate Diagnostics Center in Boulder.

Others gathered for the conference agreed.

``The word I've heard several times is it's incipient,'' said Gerald Meehl, a research scientist at the National Center for Atmospheric Research.

And if past years are any prediction, La Nina means forest fires.

By studying old-growth trees and examining their growth rings, researchers have marked a consistent history of fires over many decades. What they have found is that fire scars on the tree rings tend to line up with La Nina periods, according to Tom Murphree, professor of meteorology at the Naval Postgraduate School in Monterey.

``There's certainly a good chance of increased fire danger,'' Murphree said.

The other missing piece of the puzzle is whether the Santa Ana winds - the bane of Los Angeles firefighters - will blow more frequently this year or any stronger than usual.

National Weather Service meteorologist Rob Krohn said a connection between La Nina and the Santa Ana winds ``has never been firmly established.''

UCLA meteorologist James Murakami, however, said Santa Ana winds tend to blow more frequently in La Nina years - although no one is sure why.

``The connection behind it isn't very clear,'' he said.

Santa Ana winds are caused by high-pressure systems that linger in the desert in Utah and Nevada and push superheated air toward Los Angeles and Southern California. Once these winds reach the canyons, their speeds pick up dramatically.

Combine the winds with dry weather and huge amounts of kindling, and the results can be explosive. However, firefighters said that record-breaking heat hitting Los Angeles this week likely won't accelerate the start of fire season unless the high temperatures linger for weeks. That's because there is little wind but relatively high humidity.

``If all the factors stay the way they are, it's going to get a little drier but not make much difference in a couple of days,'' said Chief Mike Wilkinson of the L.A. County Fire Department's forestry division.