100 Inches of Snow!

And other myths about La Niña and this year's snowfall.

"Rumors of Disastrous Winter Amount to Irresponsible Hype," screamed the headline of an October press release from the University of Washington. The rumors in question, "sent by e-mail and citing official-sounding sources," the release explained, "include completely false statements about effects from the current La Ni�on the kind of winter the Northwest is likely to experience this year.

Well, city folk who drive to work were no doubt relieved to learn that Seattle and vicinity aren't in for three months of sub-freezing temperatures and 100 inches of snow. But there is a subset of the populace—equipped with four-wheel-drive vehicles and custom ski racks—that was disappointed, to say the least, by the university's hoots of derision. If Seattle had gotten 100 inches, they grumbled, what would the slopes at Crystal have been like?

Well, don't despair yet, ski buffs. We may not be in for millennial snows, but the slowly evolving science of long-term forecasting indicates that we're entering a climate phase distinctly favorable to Northwest fans of the white stuff. In the foreground, there's the undoubted fact that after a fairly powerful swing in the Central Pacific toward "El Ni�A>" conditions—warmish and dryish in the Northwest on average—we're well back into a moderate "La Ni�A>" phase, with higher than average precipitation and cooler than average temperatures.

Only problem is, predicting just when that precip is going to fall is not only impossible for current forecasting techniques, but probably impossible in principle. "Our weather patterns are determined by the course of the jet stream," says Philip Mote, one of the climatologists in charge of shooting down last month's urban-snow legend. "We can say with fair certainty what the average course of the jet stream is going to be for any given winter, but predicting its exact course is as impossible as predicting the motion of a high-pressure fire hose when nobody's holding onto it." Still, according to records kept for Rainy Pass on the North Cascades Highway, total snowpack in these parts corresponds closely with the Ni�Ni�wings over the same time period.

In recent years, another team of UW scientists has been on the track of another temperature variation in the Pacific that deeply affects our weather, this one centered in the North Pacific near the Aleutian Islands. The so-called "Pacific Decadal Oscillation" (PDO for short ) is even less predictable in the short term than Ni�i�but it may be more important for the Northwest, affecting everything from salmon runs to stream flow from Bristol Bay to the mouth of the Columbia and beyond. The word "decadal" is a little misleading, since the oscillation, at least since 1900 when record-keeping gets refined enough to track its traces, seems to average closer to 20 years per phase.

If the rough pattern since 1900 holds up, we departed a 13-year swing toward lower total snowfall around 1990. The upswing toward higher average snowpack (with major, unpredictable variations from the average), could well last that long or longer. So try to look on the bright side, skiers: In the long run, things are going your way.

Related Links:

UW press release debunking "100 inches in Seattle" rumors

Generic La Nina info (non-technical)

Pacific Decadal Oscillation (detailed but not technical)

General el Nino information (mostly links)

Cool El Nino/La Nino animation

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