Sisters Country winter: How did the forecasters do?

Last fall, before an attentive audience at the Oregon Museum of Science and Industry in Portland, four weather and climate specialists talked about the kind of weather we might expect here in the Pacific Northwest for the upcoming winter season.

They were Kyle Dittmer of the Columbia River Intertribal Fish Commission, Pete Parsons of the Oregon Department of Agriculture, George Taylor of Applied Climate Services, and Tyree Wilde of the National Weather Service.

A central theme in all of these forecasts was that El Niño (a warming of sea surface temperatures in the tropical central Pacific Ocean) would hold sway through the winter.

When an El Niño is in effect, broad-scale weather patterns are altered in such a way that usually results in warmer and drier than normal winters. A cool and wet early season typically warms and dries by mid-to-late winter.

The El Niño signature was weak last fall, and three of the four prognosticators thought it would remain so throughout the winter, maybe even disappear entirely by season's end. This group forecasted close to normal temperature and precipitation levels. The likelihood of a December arctic air outbreak was also part of this mix.

The lone holdout said El Niño would strengthen as winter progressed. He foresaw a decidedly warmer and drier winter.

Now that winter's over, let's use the benefit of our 20-20 hindsight to evaluate how well the clever clairvoyants did:

Winter did indeed get out of the gate early. Although precipitation was slightly below normal across Central Oregon in November, freezing levels were low and enough snow fell in the mountains to allow ski resorts to open early. Skiing began at Hoodoo Mountain Resort on November 27, about 10 days earlier than usual, according to general manager Matthew McFarland.

Then during the second week of December, bitterly cold air from extreme northwestern Canada blasted its way into our region. Weather records collected at the Sisters Ranger District office show the coldest daily minimum temperature was observed on December 8, a bone-chilling -18 degrees Fahrenheit. Five straight days of subzero readings were put in the books, but very little snow fell. We would not experience another intrusion of arctic air for the remainder of winter.

El Niño did strengthen through the fall and midwinter, reaching a peak in January. This produced a characteristic split flow in the jet stream that sheared apart approaching Pacific storms, sending most of the energy northward into Canada and southward into California. Many of these storms continued eastward through the southern tier of states bringing heavy snows to the mountains of California, Arizona and New Mexico, and flooding downpours at lower elevations in Texas and the southeastern states - yet another El Niño trait.

Meanwhile, the Sisters Country was left mostly high and dry. During the four-month period December through March, we came up two inches short on precipitation here in Sisters. Although temperatures were somewhat below normal for the same period, the brief cold snap in December was not representative of the winter as a whole. Disregarding the arctic air anomaly, the average temperature comes in significantly above normal.

This warmer and drier theme was also reflected in Central Oregon's Cascade snowpack. It was only 66 percent of normal as March ended, according to Marilyn Lohmann, hydrologist at the National Weather Service in Pendleton.

But by then El Niño was beginning to loosen its grip. As April burst on the scene, so did a series of low pressure systems from the Gulf of Alaska, supported by a more consolidated jet steam. The result was a cooler and wetter than normal April. And the snowpack improved to 81 percent of normal by month's end.

So, how did our fearless forecasters do? They get high marks for winter's early start, December's frigid temperatures, and a moderately strong El Niño. Well done, boys.

Ron Thorkildson is a retired meteorologist who lives in Sisters.