Outdoors

Mark Morical: Predicting winter’s snowfall is tricky

Gazing west from Bend toward the newly snow-covered Cascades, many of us are dreaming about the upcoming ski and snowboard season.

This time of year is filled with things to whet the appetite of snowriders: ski swaps, skiing and snowboarding films, deals on new gear.

But just what sort of winter can we expect this year in the Central Oregon Cascades?

That is a hard question to answer every year, but maybe even more so this year.

Larry O'Neill, interim director of Oregon Climate Services at Oregon State University in Corvallis, says there is an above-average chance that this winter will be warmer than normal and that precipitation amounts are projected to be average.

"As far as snowfall goes, it's really hard to say," O'Neill says.

"Right now the El Nino is in a neutral pattern. For the Pacific Northwest, it's kind of a mixed bag, what we get after that, whether we get a good or poor snow year."

El Nino – which usually makes for a warmer and drier Northwest winter – and La Nina are season weather patterns driven by sea surface temperatures in the Pacific Ocean.

Accurately forecasting the weather can be extremely difficult, especially without a strong El Nino or La Nina signature, but O'Neill is betting on a warmer-than-average winter in the Northwest.

Another climate pattern that O'Neill says affects our snowfall is the Arctic oscillation. He says that pattern has been shifting farther north of Central Oregon. That could continue for the next few weeks, and possibly the next few months, he notes.

"Usually in the positive phase of the Arctic oscillation, the snow accumulation tends to be less," O'Neill says. "Of course that's subject to change. But right now if I were to venture a guess, I'd say the Cascades might be a little bit warmer than normal and probably slightly less snow than normal."

Last winter, Central Oregon was hammered with about 3 feet of snow in late February, and the snow stuck around on the ground for nearly a month. That made for stellar spring skiing at Mt. Bachelor ski area and Hoodoo Ski Area.

O'Neill says the nearly 10-year trend of significant late winter/early spring snowstorms will likely continue. Last winter brought a moist storm on top of a cold Arctic air mass that produced that late-season snowfall.

"The last five to 10 years we have gotten into this pattern where the end of winter, beginning of spring we get a burst of precipitation," O'Neill says. "And then the middle of winter, when we used to get most of our precipitation, we actually get these blocking ridges that set up with no big storms to ride over the top. That seems to be a persistent pattern, and if I were to guess, it almost seems like we're starting to follow that pattern again. I would say there's a decent chance that happens again."

O'Neill adds that this trend includes snowfall in middle to late autumn as well, before the ridges of high pressure set up and make for a mainly dry December and January. These ridges, O'Neill explains, split the jet stream and, leading to weaker storms and less precipitation.

He says the blocking ridges could become stronger and more frequent in years to come.

"What's bad is we get a couple feet of OK snow in December to sort of ski on, and then it just shuts off," O'Neill says. "So if you don't get in on it right when it happens, you have to wait until February or so when the next storm comes in."

O'Neill says this trend, along with freezing levels slowly moving higher in elevation, is associated with climate change.

"The precipitation patterns are shifting," he says. "At times we're getting these earlier rain bursts in October, when before it would have fallen as more snow. The trend now is for it to fall as rain."

It has been a challenge for smaller ski resorts like Willamette Pass (base elevation 5,128 feet) and Hoodoo (base elevation 4,668 feet) to remain open when the blocking ridges set up in the middle of winter and when precipitation falls as rain and not snow.

"Being right at that elevation, just a 500-foot shift in the snow elevation can mean the difference between a lot of rain and a lot of snow," O'Neill says. "It's been really challenging. The projections are for that to continue. Hoodoo's a little bit better because they have a microclimate where they get a little more snow. Willamette Pass is in a part of the mountains that's really unpredictable – south-facing and snow melts faster."

Bachelor – which typically opens around Thanksgiving – is largely immune to this problem because of its relatively high elevation of 6,300 feet at its base and its position on the eastern edge of the Cascades. The air on the east side of the Cascades tends to stay colder, which helps bring snowfall and helps it stick around.

"The Cascades have more cold-air damming that occurs up against the east side of the mountains," O'Neill explains. "More of the Canadian air will settle in there and it's consistently colder. Snow at the crest of the Cascades or slightly west gets washed with warmer marine air."

While every winter is unpredictable, we do know that the snow will come at some point. So wax those skis and boards and prepare for another season on the slopes, no matter how much snow there might be.

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