OREGON STATE UNIVERSITY

Forecast: Analog year could mean extreme weather events

09/06/2005

CORVALLIS - Climate forecasters predict the future by examining recent sea surface temperatures, regional climate patterns, and even Atlantic Ocean hurricanes - and this year these indicators show a close similarity to conditions prior to the winter of 1995-96.

If such a pattern holds true, says George Taylor, this winter in Oregon could be a doozy.

Taylor is a faculty member at Oregon State University who serves as the state climatologist. He said the 1995-96 fall and winter will long be remembered for a powerful wind storm in December, two ice storms, and the massive "100-year flood" in February, which closed schools, isolated communities, and caused millions of dollars of damage.

"It was a wild year," Taylor said. "And because there is a strong correlation between conditions during the first several months of this year and early in 1995, it would appear the chances for an extreme event this winter are quite high."

Every year Taylor makes a prediction for fall and winter weather based on a number of factors, culminating in selecting "analog years" that most closely resemble current conditions. He takes into account long-term wet and dry cycles (known as the multi-decadal phase), El Nino and La Nina episodes, sea level pressures, temperatures, wind speeds, solar cycles and even hurricanes, which have a surprisingly strong correlation to Northwest climate.

"Based on a composite of analyses, we are usually able to identify four or five analog years that had similar conditions during the first several months of the year, which helps us predict what the weather may be like in the fall and winter," Taylor said. "The 1995-96 year was weighted twice as strong as any other year.

"That doesn't mean the outcomes will be similar," he warned. "Let's just say things are leaning in the direction of extreme events and that an active year seems likely."

Taylor said the trend this fall and winter appears to be warmer and wetter than normal, throughout the state:

  • Oregon Coast: Temperatures will be above normal October-December and January-March; precipitation will be near normal October-December and above-normal January-March.
  • Willamette Valley: Temperatures will be above normal October-December and January-March; precipitation will be slightly above-normal October-December and above-normal for January-March.
  • Southwest Interior: Temperatures will be above normal October-December and January-March; precipitation will be slightly above-normal October-December and above-normal for January-March.
  • Northeast Oregon: Temperatures will be above normal October-December and January-March; precipitation will be slightly above-normal October-December and above-normal for January-March.
  • Southeast Oregon: Temperatures will be above normal October-December and January-March; precipitation will be slightly above-normal October-December and above-normal for January-March.

    Other analog years for 2005-06, and their extreme events, include 1952-53 (flooding and wind storms); 1973-74 (flooding); and 1969-70 (ice storms).

    Last year Taylor predicted a wet, early fall despite a summer drought and was right on the mark. He also correctly predicted a wet spring. But, he added, "we experienced a very dry mid-winter last year, and that is something we never anticipated."

    Taylor said every year his most frequent request is to predict whether it will snow in the low elevations. Every year, he disappoints his followers.

    "Snow is just so hard to predict," he said, ruefully. "The only thing we can say is that there's a better chance of snow after Jan. 1."

    In his annual forecast, which is available online at http://www.ocs.oregonstate.edu/index.html, Taylor gives ample room to his "competitors." The Country Farmers Almanac, for example, predicts snow flurries as early as December and "true winter weather" in February with severe snowstorms. Harris Almanac offers a forecast that is generally cooler and slightly drier than Taylor predicts. And the Old Farmers Almanac predicts a comparatively warm and wet winter - somewhat in line with Taylor.

    "Now we just wait and see what happens," Taylor said.