CORVALLIS - An exceptionally strong but early-peaking El Nino event will bring early precipitation to Oregon this fall and winter, but the first couple of months of 1998 should be drier and warmer than normal, according to Oregon State University's George Taylor, the state climatologist.
Taylor and Tye Parzybok, an OSU research scientist, have just released their forecast for the fall and winter of 1997-98.
During the past five months, an El Nino has developed in the Pacific that may be one of the strongest this century, said Taylor, who is on the faculty of OSU's College of Oceanic and Atmospheric Sciences. Sea surface temperatures are a staggering nine degrees higher than normal off the coast of Peru, where scientists say El Nino events originate.
This El Nino may, in fact, rival the event in 1982-83 in intensity, Taylor said, but it has different characteristics that likely will result in different weather patterns.
"Typically, an El Nino will produce a drier and warmer than normal winter in the Northwest, but occasionally a very strong event will bring wetter than normal conditions," Taylor said. "This happened in 1982-83, but that event peaked late in the winter. There are indications that this El Nino peaked in June and may be beginning to wane."
Taylor said this year's pattern seems to more closely resemble 1977 and 1972. Both years had interesting winter weather.
In 1972, an extremely cold air mass settled over Oregon in December. Salem recorded its all-time low temperature of -12 degrees, and the entire Willamette Valley had below-zero temperatures and a foot or more of snow. In eastern Oregon, many sites recorded temperatures of -30 degrees, led by Seneca with a numbing -40.
In 1977, a series of very strong storms hit western Oregon in November and December, bringing high winds, heavy rains and snow to the state. Portland received eight inches of snow.
Such weather conditions may occur again, Taylor said. While early September is expected to be cool and unsettled, the weather will turn "pleasant and mild" by mid-month and extend into October. But by mid- to late-October, the first significant winter storms are expected to bring rain, wind and much cooler temperatures.
"The active polar jet stream and the abundance of moisture from the warm, equatorial waters will help spawn several potent mid-latitude storms in the northern Pacific Ocean during November and December," Taylor said.
"Several of these storms should affect Oregon, producing cold temperatures, high winds, moderate rains and mountain snows," Taylor added. "While the storms are expected to be powerful, we do not expect extreme flooding as we did in past winters."
Skiers, however, should not begin celebrating the early snows just yet, Taylor pointed out. Latest forecasting models call for the jet stream to move northward in January, leaving Oregon with drier and warmer conditions.
The storm track likely will split, Taylor said, sending powerful, subtropical storms into California with southern Oregon occasionally receiving "glancing blows." The northern branch of the jet stream will affect British Columbia and Alaska, leaving most of the Northwest dry and mild through February.
Conditions can change, Taylor said. Scientists are watching a large, cool sea surface temperature anomaly located about 2,000 miles off the Oregon coast.
"Anomalies such as these can have an impact on the weather, but at this point, the effects are unclear," Taylor said.
Overall, seasonal precipitation will be fairly close to normal. But most of the rain - or snow - is likely to come early in winter, with drier, warmer conditions later.
Additional climate and weather information is available on the web site of the Oregon Climate Service at Oregon State University. The address: http://www.ocs.orst.edu
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George Taylor, 541-737-5705