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CORVALLIS, Ore. - Enjoying all that warmth and sunshine? Well, now might be a good time to batten down the hatches, tend to those roof repairs you've been putting off and make sure everyone has a cozy warm coat going into this winter.

In all likelihood, it's going to be a nasty one.

According to the newly-released fall and winter climate forecast of George Taylor, the state climatologist at Oregon State University, a full-blown "La Nina" is about to send a series of cold, wet winter storms rolling into the Pacific Northwest and, generally, the northern half of the United States.

"Compared to last year's comparatively mild winter, it's going to be a lot colder with a high level of precipitation," Taylor said. "This is shaping up to be a potentially severe winter."

As the much-ballyhooed El Nino wanes, Taylor said, it is being replaced by a significant "La Nina" event, which will overlay its own weather impacts on top of a 20-25 year "wet cycle" that the Pacific Northwest entered in 1995.

It's too soon to predict whether the severity of precipitation will lead to the deadly, destructive floods that deluged western Oregon and Washington in 1996 and 1997, Taylor said. In Corvallis, Ore., 1996 was the single wettest calendar year in the city's history, when 73 inches of rain fell instead of the average of 43. But "it's safe to say it's going to be significantly wetter than average," Taylor said.

Among the specific predictions for Oregon:

• The state will probably experience wetter than normal conditions from October through December, and at least normal or wetter than normal precipitation later in the winter.

   

• Some of the early moisture will be tropical storms on a path from Hawaii, major rain events that have in the past been called the "Pineapple Express." .

   

• Temperatures should be near normal through December and then become colder than normal from January through March.

   

• There's a strong possibility of above average snowfall in the mountains and an increased likelihood of significant snow in the Willamette Valley and other western valleys.

   

• The climate should present good ocean and stream conditions for salmon.

While the skiers rejoice and everyone else slowly goes stir-crazy from the lack of sunshine, an explanation for the weather will be found thousands of miles away in the equatorial Pacific Ocean, Taylor said.

Ordinarily, upwelling currents off South America yield cold water temperatures of about 68 degrees, while at similar latitudes off Indonesia the ocean might be as warm as 88 degrees. During an El Nino, Taylor said, prevailing trade winds break down and the ocean near South America becomes much warmer. Among other global climatic impacts, this often leads to a mild winter in the Pacific Northwest.

But during a La Nina, the ocean temperature near South America is even colder than usual and the tropical waters in the western Pacific Ocean are like a giant hot tub. This holds implications for the Pacific jet stream, shifts in wind, precipitation patterns and other climatic variables.

And usually, during this pattern the northern United States gets socked with harshly cold, wet winters, while the southern half of the nation is comparatively warm and dry.

"As we learn more about these phenomenon the correlations become more clear," Taylor said. "None of this is a certainty, but in terms of temperature we can predict general trends during a La Nina with about 80 percent reliability, and with precipitation we're about 70 percent sure."

The 20-25 year wet and dry cycles that Taylor endorses also play a heavy role in these phenomenon, he said, with more El Ninos during the dry years and more La Ninas during the wet ones. For instance, a 20-year dry period for the Pacific Northwest that ended in 1995 was correlated with six El Nino events and only one La Nina.

By contrast, since 1994 we've already had two La Ninas - and if the cycle theory holds merit , more may be on the way. The last wet phase, from the late 1940s to the early 1970s, was characterized by mostly wet, cool winters in the Northwest.

"The large floods we had two years ago occurred during a La Nina event," Taylor said. "That was not a coincidence. That doesn't mean we can predict these climate patterns for sure. But this analysis is a lot better than flipping a coin or turning to the Farmer's Almanac."