Last year Mother Nature ignored expectations, providing the Columbia River Basin with a better than average snowpack and water supply to buoy fish, water crops, generate power and provide for other water uses.

Most long-range forecasts had called for an average year, or mild La Nina, at best.

This year weather signs are tilted toward a warmer and drier than average fall, winter and spring seasons.

But don't count on another season of exceeded expectations, say experts gathered Tuesday in Kelso , Wash. , at the winter 2006-2007 climate and water supply forecast meeting sponsored by the University of Washington 's Climate Impacts Groups.

A moderate "El Nino" condition has developed over the summer in the tropical Pacific, and history shows such conditions usually remain stable into the New Year, according to Alan Hamlet, a UW research scientist.

The experts acknowledged that the winter could be wet and cool despite the signs, but said those El Nino influences are becoming entrenched and could grow in strength to the point that a resumption of drought may be in the near future.

As the El Nino condition continues to strengthen, those odds grow.

"We have a heightened risk of drought" if El Nino weather prevails, Hamlet said.

"It's all about the tilt in the odds," Nathan Mantua of the University of Washington said of the climatic variables used to make weather forecasts.

Long-range forecasters have judged the El Nino/Southern Oscillation phenomenon to be in an El Nino phase. La Nina ENSO signals boost the odds for cooler, wetter seasons.

Other factors could counteract the El Nino conditions, which have at times seemed to help push up a strong low pressure system off the Northwest coast. It blocks the normal jet stream that pushes storm systems into the region from the west. If the low sets in, the storms typically have a north-to-south orientation.

Typically, less moisture is wrung from such southbound storm clouds than those hitting the Northwest directly from the Pacific Ocean , Mantua said.

An average or moderate El Nino usually results in about 10 percent less precipitation through the Northwest's wet season.

The precipitation patterns shifts somewhat as well, Mantua said. During an El Nino year, the west slopes of the Cascades and Rockies get less moisture.

"You can still have above average precipitation in the dry parts of the Columbia Basin ," the "rain shadow" on the lee side of the mountains, Mantua said. But a little more precipitation in those, for the most part, arid areas does little to improve the overall precipitation picture.

El Nino is rooted in the waters of, particularly, the western equatorial Pacific. Water is averaging between 1.5 and 2 degrees C warmer than normal now. It has been slowly warming since May, and slowly eroding cooler waters to the east.

"The warm pool has sloshed over" to expand its influence, Mantua said. "The warming isn't over yet." He predicted it could continue into November or December before waning.

"The ENSO signals we're getting are very robust," Hamlet said. Usually, the phenomenon begins with summertime warming of those tropical waters with a peak being reached in midwinter. El Ninos generally disappear by the next April or May.

Once the water temperature trend begins, it takes time or dramatic climatic events to halt or reverse its progress. For example, uncharacteristically strong winds, particularly from the west, can have an effect.

The region goes into the new water year parched, but not abnormally so for this time of year.

"Everything looks pretty normal," said the UW's Andrew Wood. Soil moisture is at its low annual ebb, but not extraordinarily so despite a hot, dry summer. Reservoirs are low too but that is almost always the case in the fall.

"It's not as bad as last year," Wood said, when drought conditions prevailed across much of the Northwest. The unanticipated La Nina conditions turned the odds toward rain and snow in the fall and winter. Fall rains absorbed much of the drought. Snowpack built to above-average levels then began melting off a bit earlier and more rapidly than usual. Most was gone in July.

"We had consistently wetter conditions than we expected" through the fall and winter, Hamlet said.

"This was a very unusual event," Hamlet said of the switching of ENSO signals last year. "It suggests to me that it was a wind driven event" that helped cool the tropical waters.

The "water year" ended unusually too. Idaho , Oregon and Washington collectively during May through July were "the warmest on record," Mantua said. The June-August period was the third warmest.

With a relatively normal starting ground, Wood employed Ensemble Prediction System (ESP) modeling to compare potential April through September stream flows next year in the region under neutral conditions, and if the El Nino effects are realized.

At the The Dalles Dam, the outcome was 100 percent of normal stream flow in neutral ENSO state, and 88 percent with El Nino. The Dalles , in the lower Columbia , passes most of the flows from the Columbia/Snake river basin. At Priest Rapids Dam on the mid-Columbia the forecast was 101 percent vs. 89 percent; the Snake output would be 96 percent of normal without El Nino and 83 percent with.

Most of El Nino's stream flow effects are felt primarily April through July. Wood's modeling comparison indicated the Upper Snake flows during that period would be 95 percent of normal in a neutral condition and 83 percent of normal under El Nino conditions. The Pend Oreille River differential would be 99 percent vs. 84 and the Mica Reservoir flow would be 101 percent vs. 93 percent. The Pend Oreille , a tributary to the Columbia , is in north Idaho . Mica is in the uppermost Columbia Basin in British Columbia .

Wood admitted that Oct. 1 is very early in the season for forecasting.

"A wet month in November or December" could greatly tilt the percentages, he said.

The Climate Impacts Group engages in climate science in the public interest, working to understand the consequences of climate variability and climate change for the Pacific Northwest , according to an overview on its web page. CIG's focus is on the intersection of climate science and public policy -- performing basic research aimed at understanding the consequences of climate fluctuations for the PNW, and promoting application of this information in regional decisions.

The CIG includes representatives from a variety of UW schools and colleges -- Atmospheric Sciences, Marine Affairs, Forest Resources, Aquatic and Fisheries Sciences and Civil Engineering.

CIG each fall sponsors workshops highlighting the seasonal climate forecast and water resource outlook for the region for the upcoming water year. The Kelso session drew 60 participants, including water resource managers, power supply managers, fisheries managers, and others. In addition to presenting climate and water supply forecasts, other speakers described advancing forecasting methods and tools and addressed potential effects from climate change, such as global warming.

In addition to CIG personnel, presentations were made by representatives of NOAA's National Weather Service, the Bureau of Reclamation and U.S. Geological Survey, the National Resource Conservation Service and NOAA's Northwest River Forecast Center .

CIG will sponsor an Idaho climate and water forecast meeting on Oct. 17 at the Idaho Department of Water Resources, 322 E. Front St. , in Boise .