What Does A La Nina Winter Mean For Snow Sports?
After seeing a web cam shot of snow-covered Mt. Washington, NH this past weekend, I quickly contracted a case of “calendar shock”, realizing that it was time to submit some ideas on where I think this winter is headed, weatherwise. Co-Publisher Mike Maginn wrote a nice piece on La Nina earlier this month and indeed, this will be a La Nina winter. La Nina is the cold water cousin of El Nino, with the waters of the equatorial Pacific Ocean running below normal now and likely to remain that way through much of the upcoming winter. What does that mean in terms of sensible weather downstream over the U.S. and Canada? Well, there are different flavors of La Nina, based largely on how cool, relative to normal, those tropical waters are. This looks to be a weak to moderate La Nina, and in general, the storm tracks during a La Nina winter look like this:
You will notice that most of the storm tracks are over the northern half of the country, closer to the source of cold air that makes those systems productive in terms of snow. La Ninas are not as friendly as El Ninos to skiers and riders over the southwestern quadrant of the country, thus, the lack of an established tendency. Well before the first turns of any season, friends and clients often ask me for guidance on where to head in the West for a winter trip. During a La Nina, I steer them north of I-70, where the busier storm tracks lead to more snow and more consistent conditions. There are exceptions, but the resort snowfall data that Mike included in his article supports that idea.
As far as La Nina winters over the Midwest and East are concerned, we often see a battle between a cold jet stream level trough over the center of the continent and a warm southeastern ridge. A preview of that set up will develop during the last week of this month. Take a look at this forecast for the jet stream valid on 10/28.
During winter, large dips in the middle of the country will act as a receptacle for cold air moving southward out of Canada. As troughs interact with warmer air along the Gulf and in the Southeast, storms often take shape and then move northeastward along the western slopes of the Appalachians, as you can see on the storm track map above. These storms bring snow to resorts in the Great Lakes, both from the low pressure center, and from backlash lake effect snow once the low move up into Canada. The storm track that you see east of the Appalachians comes from systems that redevelop east of the mountains as the upper trough moves toward the coast. These are known as “secondary” low pressure centers, formed as the upper level support translates over the mountains and taps into energy from the waters of the Atlantic. These secondary storms represent the best opportunities for meaningful snowfall at the resorts of the mid-Atlantic and Northeast during a La Nina.
There are other factors that are correlated with subtle but potentially significant changes in these storm tracks, one of which is the solar cycle, and I will discuss those factors in the coming weeks. For now, though, I am most bullish on the prospects for the West, north of I-7o and the upper Midwest. I am guardedly optimistic about the Northeast, where temperatures should work out slightly milder than normal but with above normal snowfall via some sizable storms. The anticipated southeastern ridge will likely pose some problems for the Mid-Atlantic and especially for the Southeast.
Yes . . .