BRRR, IT'S WARM OUT MOTHER NATURE MIXES IT UP, BLOWING HOT THEN COLD IN THE SOUTHLAND.

Byline: Erik N. Nelson Staff Writer

It rained last Monday. Record cold hit on Wednesday. Friday the winds came, heating the San Fernando Valley back up to T-shirt weather so Saturday was nice, Sunday a bit cool.

What's with this crazy weather?

Call it La Nada.

There's no El Nino or La Nina to speak of like there were the last couple of years, so Southern Californians are at the mercy of, well, the weather. And weather, as most people in the rest of the country know, is always changing.

This year the Pacific Ocean waters near the equator are not warmer than usual (El Nino) and not too cool (La Nina), so the Southland is expected to receive its normal allotment of rain.

Much to the delight of street lugers and picnickers, normal is less than 15 inches for the season in downtown Los Angeles. The most recent El Nino winter, of 1997-98, dumped 31 inches of rain downtown.

The weather swings have been prompting other explanations as people dig out their sweaters in the morning, only to tie them around their shoulders as the sun rises in the sky.

``I'm wondering if it's from the polar ice, if it's starting to melt, with global warming and all,'' said Pamela Lincow, a 20-year-old Pierce College student out for a stroll Friday near the Los Angeles River in Balboa Park. ``I want to take advantage of the sun - while we have it.''

Just don't blame the loopy weather on El Nino or any of his climatological relatives, said Tim Barnett, climatologist at the Climate Research Division of the Scripps Institution of Oceanography in La Jolla.

Barnett is an expert on the El Nino Southern Oscillation, which, put simply, is a warming of Pacific Ocean water near the equator, combined with other factors such as barometric pressure differences.

El Nino causes unusual weather all across North America. In Southern California, it usually causes stormy wet weather.

The last El Nino doubled the area's normal precipitation and set seasonal rainfall records.

This summer, Barnett predicted ``a very weak'' El Nino for the winter that starts Dec. 21, but water temperatures are currently close to normal and even on the cool side.

A northern Pacific water temperature condition called the Madden-Julian Oscillation is expected to increase chances for storms and flooding in the Pacific Northwest but won't impact Southern California, Barnett said.

Since 1970, there have been five major El Nino events, sometimes followed a year later by La Nina, or cooler Pacific water that helps keep the Southland drier. There have been three major La Ninas since 1970, including the last two winters.

Interest in the ocean's impact on weather is so keen that the National Aeronautics and Space Administration launched a satellite Friday from California's Vandenberg Air Force Base that will spend much of its time monitoring the temperature of Equatorial Pacific waters.

Without one of those two conditions, Angelenos are at the mercy of more fleeting weather patterns, such as last week's.

``If we're in El Nino or La Nina conditions, it's much easier to predict the weather conditions,'' said Steve Taylor, who is writing a doctoral thesis at the Scripps Institution on the impacts of climate change on wind and waves along the Southern California coast. ``If we're in normal conditions, it's much more difficult to predict the weather.''

One of the people who's most familiar with Valley weather wasn't the least bit fazed by last week's week's weather extremes.

``It's a fairly normal pattern,'' said Bill Russell, professor of geography and meteorology at Pierce College and director of the college's renowned weather station. A storm pushed by the jet stream blows in from Alaska, ``and behind it you have much colder air,'' such as that which brought thermometers in Chatsworth down to a record 34 degrees Wednesday morning.

``Once a storm passes by, and it's really clear, that allows any heat that's absorbed during the day to radiate back to the atmosphere during the nighttime,'' Russell said. The storm tends to drag a high pressure system behind it, which continues eastward into the Great Basin, where it sits and blows warm Santa Ana winds back into Southern California, he said.

This time of year, Russell said, it's not unusual to see fir trees tipping over in Christmas tree lots from the Santa Anas.

Russell added that while there's no El Nino or La Nina to affect weather in the Southland, ``I don't know that there's really a truly 'normal' winter.''

Taylor agreed, saying, ``When I lived in Santa Barbara, they used to joke that we never get the normal rainfall. It's always none at all or lots and lots of rain.''

Interestingly, Taylor believes there might actually be some truth to Lincow's supposition about global warming.

``Some people might say we're in transition now'' from lower to higher temperatures, which could cause weather swings, Taylor said. ``But to distinguish that from the natural variability would be very difficult.''

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Chart:

WINTER IN THE VALLEY

Sources: Western Regional Climate Center, Golden Gate Weather Services

Dan DeLorenzo/Staff Artist