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Sunday, November 18, 2007

Back 4 More !! – Seasonal Outlook for ’07-‘08

I always say that the approval rating of a weather guy is only as good as the weather he/she predicts. If I can’t forecast sunshine and pleasant temperatures on your wedding day then I can’t forecast my way out of a paper bag. Likewise, if I can’t predict a snowy winter for the Mad River Glen faithful then perhaps the powers that be should find someone who can ;). Don’t feel bad the sentiment is perfectly normal and I am very used to it. I am proud to be “back 4 more” or a 4th season of blog duties. It’s been a lot of fun and it’s the greatest audience. And for all those skiers who visit the blog but are still loyal to Sugarbush, Stowe or Killington; well, we are still happy to have you but would be even happier to see you buried in powder on Paradise. And for our snowboarders out there, we are happy to have you too, but I can’t provide regular updates on snowmaking, or half-pipe making in November. You will just have to get your weather from other sources until the opening bell at MRG is a few days from sounding.

If the opening sentence sounds to you like a disclaimer then your intuition is correct. There is very little to be excited about when looking at the upcoming winter from the perspective of our favorite seasonal variables. That being said, I don’t think I can do much better than 60 percent on these seasonal outlooks and I have for the most part, called the last three winters correct. This means I am overdue for a serious bust. It took one heck of a finish in 2007 to get that one into the win column but in the end the mountain tallied nearly 300 inches of snow and temperatures were slightly above normal in accordance with the pre-season prediction. There was a gentlemen (I forgot his name) who emailed me after the seasonal forecast last year and by using his favorite folklore, predicted a slow start to the winter followed by a big finish. He was even more right and should receive some well-deserved recognition.

1) ENSO – It has delivered us a low blow with the re-development of what could turn out to be a nasty La Nina.

2000-2001 quite possibly could have been the most epic winter in the history of Mad River Glen. That winter included a storm in early March which dumped 50-70 inches on much of the Green Mountain spine. Believe it or not, ENSO conditions that winter were that of a weak La Nina. 1995-1996 also featured a weak La Nina and MRG was graced with Mother Nature’s better half for much of the winter. Moderate to strong La Nina’s, such as the one threatening to prevail this winter, do not have a particularly good relationship with us MRG skiers. Some of the stronger La Nina winters include 1999-2000, 1998-1999, 1988-1989 and a string of winters during the early to middle 1970’s. Vermont typically fairs substantially better than locations further south during moderate to strong La Nina’s. Locations such as West Virginia for instance often feel the effects of a potent southeast ridge in the Jet Stream, which aside from making it incredibly mild for long stretches of the winter, also deflect storms to the north and west, which means little if any natural snow. Snow often does fall in New England but very often the snow events also include mixed precipitation or rain. We were blessed with 58 days during the second half of the 06-07-ski season without rain, an occurrence, which made last season one of my personal favorites. It is very unlikely that we will even get 30 days without rain unless La Nina subsides. Currently the critical 3&4 Nino regions are seeing SSTs of 1.3 C degrees below normal, which in a quantitative assessment is as a moderate to borderline strong La Nina. SST’s would need to warm to at least within a degree of Celsius before we can categorize the ENSO event as weak.

Round 1 - The current state of La Nina favors below normal snow and normal temperatures. A La Nina such as this one is often a knockout upper cut to the ski areas in the Middle-Atlantic but interior New England does tend to fair better but far from great.

2) Pacific Decadal Oscillation (PDO) – This is measured as an index and the October value was an ugly -1.45.

We can again start this part of the analysis on a positive note by recalling the winter of 1970-1971. This is one winter that ranks right up with 2000-2001 in the epic category and a winter where the PDO index was close to -1.70 (see link below).

In general, however, there has been a correlation between the index of the PDO and the prevailing weather pattern for eastern North America and this correlation would have us hoping for a more positive index as opposed to the -1.45 recently recorded. There is some very general information on the PDO that can be obtained through Wikepedia.

More specific information including the page that actually tracks the indices is included here.

Both the index of the PDO and the ENSO have been known to change quite abruptly even at the 11th hour. It is often why many seasonal forecasts which are made too early in the autumn go belly up. This seasonal outlook has been created fairly late in the ball game but these variables still have some time to do some shifting. Unless they do however I think we are in trouble.

Round 2 – The current negative index of the PDO favors both below normal snow and above normal temperatures.

3) Snow cover area – One of my favorite seasonal indicators when looked at hemispherically. When measured in millions of square KM the normal snow cover area in October is 17.7. Last year we recorded an October number of 19.8 but this year its closer to 16.3. Yuck !!

The measure of a winter from the standpoint of temperature is usually determined by the following tongue twister. The strength of the cold embedded within the cold pattern. The “strength of the cold” refers to the arctic air originating near the poles. Arctic air of a stronger intensity in a fundamentally colder than normal pattern may mean the difference between 5 degrees and 15 degrees below normal. Likewise, a normal pattern may be 5 degrees below normal instead of 5 degrees above and the adverse impacts of an above normal pattern may very well be significantly mitigated. The opposite if of course true if the air with polar origins is weaker than expected. It is important to examine this issue in any seasonal outlook because the most basic assumption that needs to be made is that the winter will consist of both fundamentally mild or unfavorable patterns for us MRG skiers and fundamentally cold or favorable patterns. 2006-2007 was a winter where us New Englanders got a good look at both sides of the spectrum.

So what does snow cover in October indicate about the measure of cold in an upcoming winter? It has to do with cold pooling efficiency. A greater coverage of snow in the polar regions early in the year will allow arctic air to strengthen quicker and reach a greater maximum intensity. An analogy can be drawn between the effects of snow cover on arctic air and the effects of anomalously warm water has on hurricanes. 2005, the year which featured Hurricane Katrina among many other land-falling storms, was defined by warmer than average water temperatures in the Caribbean and Gulf of Mexico. Storms traveling through these areas strengthened quicker and reached a greater maximum intensity. Arctic air has a similar relationship with snow cover.

Round 3 - 16.3 millions of square km is a very ugly number snow cover number. It is worse in fact than what we saw in the autumn months of 2001 and in 2005, which preceded two not-so-friendly winters. To put it mildly, the data favors above normal temperatures and when combined with some of the aforementioned indicators, I would be very surprised to see temperatures average below normal for the December to March period.

The Prediction – No spin here at the Single Chair Weather Blog. We tell it like it is though admittedly I am hoping to be dead wrong. Temperatures for the season will average above normal and significantly so. When I say significant I mean at least 3 degrees above normal for the December through March period. In terms of snow, I predicted 300 inches last year against an average of 260. This year I expect less than 220. Sorry for the lack of hype but I always like to say, if you keep expectations at a minimum you open the floor for a few pleasant surprises.