La Nina & This Winter

The first three weeks of October were sure promising, weren't they? Timberline and Mt. Hood Meadows had 2-3 feet of unsettled snow on the ground by the 20th of the month. And then... the pattern changed, and now the snow is nearly all gone. So far this fall, we've been through a very dry pattern that lasted for most of September, a very cool and wet pattern that prevailed during the first 2/3's of October, and lately we've endured a very dry pattern again that is beginning its third straight week. Lots of variety so far... and I believe there's more variety to come. It has to do with La Nina. Read on...

It seems that there is a lot of excitement in the air about the La Nina episode that has developed in tropical Pacific Ocean. For those unfamiliar with La Nina, it's a recurring (every 5-7 years) phenomenon characterized by stronger-than-normal easterly trade winds over the equatorial Pacific Ocean. The result is an area of cooler-than-average ocean temperatures in the central Pacific that, in turn, affects weather patterns over much of the Pacific. Historically, the stronger the La Nina episode, the stronger the winter jet stream, which often means lots of Cascade snow as storms are frequently directed at the Northwest. Hence the excitement about this year's La Nina.

But not so fast. According to snowpack data compiled and posted at one of my favorite websites (www.skimountaineer.com), La Nina episodes don't always lead to big snow years in the Northwest. In fact, of the 11 "weak" La Nina episodes since 1950, during only 5 of those winters did the total seasonal snowfall at Government Camp exceed the long-term average. Several of those years featured below-normal snow -- including the dreadful 2000-2001 season (Ski Bowl didn't open until January that year). But when you look at data during winters when La Nina was strongly developed, it's a much different story. Seven of the eight "strong" La Nina episodes since 1950 resulted in above-average snowfall at Government Camp. Only during the most recent strong episode (winter of 1999-2000) did Govy not reach it's average seasonal snowfall.

So... where do we stand going into this winter? La Nina conditions developed this past summer. They've persisted long enough now that this episode is a bona fide La Nina. Just this past month, the index used to the measure the strength of the episode indicated that we've entered strong La Nina territory. But that index must stay strong for several months in order for the La Nina episode itself to be classified as strong. But all indications are, at this point, that a strong La Nina is brewing. Again, hence the excitement about this year's La Nina.

If a strong La Nina is indeed developing, then above-average Cascade snowfall is a good bet for this winter. That doesn't necessarily mean the snow will come early, however. At the ski areas, of course the managers there like big snow years... but they like early snow years even better. Quality conditions at Thanksgiving and especially Christmas often determine how successful the season will be. And for visiting skiers and snowboarders, a deep, early base makes for a longer season with more boarding opportunities. I raise this point because I feel that too much emphasis & pre-season hype is placed on how much snow might fall over the course of the season -- and not enough attention is paid to when the big snow might come. Maybe that 's because when is a much more difficult forecast. An early snow can come in any year... La Nina or otherwise. And the snow can start late during any year... La Nina or otherwise. (Please remember this when there's panic in the air the next time an El Nino develops...)

I mentioned above that we've seen a lot of pattern variety so far this fall. And that is somewhat common during La Nina episodes. My guess is that the next couple months will continue to be quite variable. I envision spells of significant valley rain and mountain snow alternating with pronounced dry spells. There are signs that the next wet spell may arrive late next week. If so, that could be the start of the real snow base-building season. (The October episode was just a tease.) And it only takes a couple really good storms to get the lifts turning.

Thanksgiving skiing and boarding on Mt. Hood is still a very real possibility this year. But I wouldn't dare call it a likelihood... not yet. What is likely, however, is that the total seasonal snowfall on Mount Hood might be above average. But as for when the snow comes... flip a coin. Heads = early; tails = late. (But the summer butterflys on the mountain did arrive about a month early this year...)

-DJ