I have always felt that being a meteorologist was a blessing and a curse. When I was very young, I was already fascinated by the weather, and the first thing I looked at in both the morning and afternoon newspapers (back in the time when there were afternoon editions) was the weather forecast in the upper left hand corner of Page 1. My knowledge of how the atmosphere worked at that time was minuscule, so all I had to rely on in the winter when that brief forecast called for rain was hope that it would be wrong. And on many occasions I would awaken the next day and be thrilled to find a blessing of white ground instead of wet streets. As time went on and my education in the ways of the weather got underway, I learned to temper my youthful enthusiasm in many seemingly promising situations...snowflakes followed by a wind shift into the southeast in my native Rhode Island spelled big trouble for snow lovers, for example. As an adult meteorologist, I have developed the ability to forecast weather patterns that are both good and bad for those of us who live to slide on snow, but maturity now helps me accept unfavorable weather with a sense of resignation. Sometimes I just know it’s not going to work out the way I would like it, and that’s where the curse comes into play...pleasant surprises are few and far between in the world of weather these days. It is with that same sense or recognition that I offer you my thoughts on how I think the winter of 2007-2008 is going to work out for skiers and riders.

The season is transitioning into winter as I write this summary. Resorts have been open in the West for nearly a month already, and several eastern resorts from North Carolina to Quebec have cranked up their snow guns and lifts this week. Normally, this would jack up my enthusiasm tremendously, but the specter of a strengthening La Nina in the Pacific serves to temper the adrenaline rush that comes with the early openings. La Nina is the opposite of the El Nino phenomenon...El Nino occurs when sea surface temperatures in the equatorial Pacific are above normal...La Nina develops as those same equatorial waters turn colder than normal, as they have during the past several months. The cooling is continuing as we head through November, and that development is critical to the prospects for the upcoming winter for much of North America. Right now, the episode of La Nina is on the cusp of going from “weak” to “moderate”, measured by the deviation from normal of the water temps. The three month running mean of the central Pacific is at -0.8 degree Celsius, and all indications are that it will be greater than 1 full degree Celsius below normal very soon. It looks as though the La Nina will maintain moderate strength until sometime shortly after the first of the year, and then it will start to weaken slowly as we head through the heart of winter. The change to moderate status is critical because previous weak La Ninas have generally been very favorable for snow lovers in North America…winter temperatures have been close to normal, or even below normal in prior weak La Nina winters, and in 1995-1996, most eastern U.S. cities recorded their all-time record high seasonal snowfall.

In looking at previous moderate La Ninas, however, the results over our continent are quite different…moderate La Ninas strongly favor above normal temperatures over much of the country, the exception being the Pacific Northwest and northern Rockies, where an energized Pacific Jet stream nails those regions with plenty of snowfall. Once that jet travels further east, it delivers modified air…modified Pacific air and not arctic air. That results in warmer than normal winters in the Great Lakes and Northeast, and especially in the Southeast. The southwest is another area of the country that experiences warmer than normal weather during moderate La Nina winters. The East is drier than normal, with the tendency for precipitation to become greater later in the winter, especially in the Ohio Valley, as the La Nina weakens and its influence recedes. The Ohio Valley enhancement of precip suggests a storm track through that part of the country, and such a track leaves the Appalachians on the warm side of the storm circulation. I see no reason to doubt that this La Nina is indeed going to attain moderate status, and if so, the following two sets of maps help to illustrate how this winter could play out. The first set shows temperatures for January/February/March (JFM) for weak and moderate/strong La Ninas.

The ONI that is in the title is the Oceanic Enso Index, which is the running mean of the water temps that I referred to earlier. Currently the ONI is at -0.8, and as I said, all indications are that it will go past -1.0 soon. The “trend” that you see on the right side is a correction that NOAA makes to account for some semblance of global warming...I happen to think that correction is statistical nonsense, and I ignore it, choosing rather to focus on the left column. The second chart shows precipitation distribution in the various La Nina scenarios...when the La Nina is moderate, the Northwest sees a significant uptick in amounts, and that is why that region is in for an outstanding season. The Northeast gets somewhat wetter, but the enhancement in the Ohio Valley is greater, and again, this suggests a storm track that is generally unfavorable for eastern resorts.

There are other global factors that have to be considered for any winter forecast, including the AMO, or Atlantic Multidecadal Oscillation, which has been in its warm phase since 1995. In looking at prior La Ninas, the phase of the AMO (warm or cold) has to be considered...the cold phase that preceded the1995 flip started in the early 60’s. the PDO, or Pacific Decadal Oscillation must also be considered…the PDO is now in its cold phase, having entered that phase in the past year or so. The 11 year solar cycle is part of the equation, and right now, we are at the bottom of the cycle, which argues for the typical warmth of a moderate La Nina to be tempered somewhat. There is a index of a shorter duration, the QBO, or Quasi Biennial Oscillation, that must be factored in, as well...the QBO is a shifting of the winds in the lower stratosphere that occurs every 24 to 30 months…they are either easterly or westerly winds. We are currently in an easterly QBO, and will be through the winter, and when combined with the solar minimum, also argues against the warmth of a moderate La Nina reaching its full potential.

To this point, this discussion has been quite technical, but I wanted to give you some idea of how complex the matter of long range winter forecasting can be. I believe that the La Nina will carry the day, but it is by no means a slam dunk. I do think that the East will experience warmer than normal temperatures, by a couple of degrees. That would put somewhat of a damper on snowmaking, especially in the mid Atlantic and southern Appalachian regions. Northern New York and northern New England are cold enough to withstand a deviation of a couple of degrees and still get their fair share of snow, but the likelihood of a storm track through the Ohio Valley and eastern Great Lakes infers that storms will be messy in the Adirondacks and northern New England. The same can be said for the resorts in western New York and the central Appalachians...they will see numerous snow to rain to snow episodes this winter. In the west, the resorts north of Interstate 70 will prosper, those south of I-70 will have a tougher time tapping into Pacific moisture. The northern Rockies and Northwest look to be in jackpot position, and British Columbia is in line for a banner year, as well.

Now, it is important to point out that those areas where I expect it to be warmer than normal will not be that way from start to finish. While September and October in developing La Ninas are warmer than normal in the eastern half of the country, November is typically colder than normal. By the end of this month, I believe that will come to pass. The cold weather will extend into December...perhaps until mid month or so, but after that, the general background of warmth should dominate through January. Shots of cold air from the arctic will penetrate the Great Lakes and Northeast from time to time, which will allow for some snowmaking from time to time, but overall, there will be a period of 4 to perhaps as much as 8 weeks where Pacific air will dominate. Later in the winter, from early to mid February on, snow and cold will be more easily attainable, as the La Nina starts to weaken. It is at that time that I think we will see the most consistent snow conditions in the eastern United States. The November/early December cold is significant in that it will give resort operators a fighting chance to stockpile snow before the holidays...if you recall last year, there was only a short window of snowmaking in early December, and trail counts at the holidays were rather low as a result…this year, there should be more terrain open, even if the holiday period turns out warmer than normal.

That’s how I see it for the upcoming season. The La Nina is going to call most of the shots, and the result will be a rather volatile season, but warmer than normal overall, with less than normal snowfall (except in the northern Rockies, Northwest, and B.C.). I admit I am a bit nervous about the current solar minimum and the easterly QBO tempering the expected effects of the La Nina. Also, I have a general lack of faith in the computer models that forecast the further cooling of the equatorial Pacific waters. If somehow the La Nina fails to attain moderate status, or stays there for only a brief amount of time, then maybe, just maybe, this old forecaster can experience one of those pleasant weather surprises of my youth.

In the shorter term, the weekend of the 10th and 11th will give operators in the Northeast a good opportunity to make snow. That will be the last window until an upper level trough arrives in the region early in the week of the 19th. That trough will stay in the East through the end of the month, due to expected blocking over the Pole and north Atlantic, which will cause jet stream features to slow down for a while. With the trough in place, colder air from Canada will flow into the region. It does not look as though it will be exceptionally cold, due to the fact that much of Canada just isn’t that cold right now, nor is northeast Siberia, where we look for cold source region air at this time of year. But, that same trough, with even a moderate amount of cold air, should be able to spin up one or two storms late this month, which would go a long way toward jump starting the season.

Last Updated Friday, November 09 2007 @ 02:24 PM