Think Snow, Tweet Snow !!!

Sunday, November 24, 2013

Big mid week storm is a mainly rain to some snow situation

With the thanksgiving holiday being one of the more popular travel periods, there has been lots of talk about the upcoming storm this week. Energy in the southern branch is going to churn up a pretty impressive weather system with lots of help from the Gulf of Mexico. With some of the coldest November weather in a decade currently in place, one could certainly envision a big dump for Vermont. Right now it looks like more of a rain to some snow event. There was a bit of back and forth with the models but there is some pretty good agreement over the last 24 hours or so to take this moist system up through the lower Hudson Valley and up through New Hampshire.  In the middle of winter, this type of track could deliver the goods, but this is still late November and its very easy to draw some very warm into the equation this early in the season. Precipitation could start as a little snow late Tuesday evening before going to a cold rain by Wednesday. Accumulating snow is still likely as the storm pushes off to the northeast later Wednesday, maybe something on the order of 4-8 inches followed by another round of very chilly November weather.

We are not getting much support from some of our favorite teleconnection indices going into December. Nonetheless, the jet stream in the eastern Pacific will remain rather loose and allow arctic air to remain on the playing field through a good part of next week. There have been hints of something significant for interior New England between the 2nd and 4th of December. We will have more on that during the middle of the week. A good event next week should have the powers-that-be at MRG talking opening.

Saturday, November 23, 2013

SCWB turns decadal and winter hinting it may have some big things in store for us !!

Some early-season winter teas' n seems to have many excited about the upcoming winter and why not, winter may be nuisance to many, but for MRG enthusiasts, tis a glorious time. With that time now approaching, the 10th season of SCWB begins (crazy that it's been that long). With snow-capped General Stark, I know it seems like the blog is getting a late start, but I try to keep updates within the confines of the MRG ski season which typically begins a bit later than some close rivals. So yes, we are beginning right on time. 

All winter seasons seem to consist of some hype. If it isn't coming from yours truly, I am sure it would take a rather effortless scouring of the internet to find someone else that is all juiced up about the upcoming snow season. But with the current month of November already providing some biting intrusions of cold weather and frequent dustings of high elevation snow, it seems even the cynics want to play with the hype machine. It is certainly refreshing to be enveloped in all these positive vibes. It is certainly been a few years since winter has started with a bang. The winter of 2008-2009 featured the last chilly November and big start to a season. A few New England veterans told me that winter felt like a "throw-back" to the old days for its propensity to unleash the full variety of weather with big temperature swings, all kinds of weather, brutal cold shots and most importantly a few winter storms. This, by the way is the 20th anniversary of my favorite winter (1993-1994). That winter started a little slow, but in spite of weather pattern that was dominated by somewhat adverse teleconnection indices, arctic air of an unusually strong intensity continuously clashed with a steady stream of southern branch energy. The result a 6-7 week stretch of continuous cold and big winter storms that would occur weekly. If you could have scored Tuesday's and Wednesday's off during that year, it was a true winning lottery ticket. 

The winter of 1993-1994 comes to mind as I have watched the current month of November play out. I recently returned from my 2-week honeymoon and I can remember looking at the weather pattern going into the month and thinking of how generally unexciting and mild it appeared, particularly as it related to our favorite teleconnection indices, the AO, NAO and PNA. Yet upon my return, the actual weather has defied all of that and the month will finish with one of the coldest thanksgiving weeks that interior New England has seen in 20 years. Sure, it may seem overly analytical to get hyper-focused on these details but I am a geek like that, and I do believe these little subtleties can provide important clues to how the weather on the mountain plays out this season. 

All of that aside, it remains vitally important to focus first on more quantifiable variables that have some proven merit. With that, let me unleash the disclaimer about how incredibly inexact the science of seasonal forecasting is, how fluid long range weather predicting can be and most importantly, how many longer range outlooks get inflated with first-rate BS. The state of the ENSO however is not BS part of a long range forecast, particularly a winter forecast. It remains one of the best ways to get a early sense of how a winter might behave from a personality standpoint. The ENSO, for the last three winters has been in a La Nina state, the last winter featuring a very weak La Nina and one that only developed midway through the winter. This winter much like last features a equatorial Pacific Ocean where sea surface temperatures are average, thus yielding an ENSO close to neutral (a positive SST anomaly yields an El Nino while a negative yields a La Nina). We have some experience with the analysis (being that we have been doing this 10 years) and the ENSO neutral winters tend to be on the colder side of a somewhat upward trending moving average of temperatures. The three worst winters for both snow and cold in the last 15 years (01-02, 05-06 and 11-12) were all La Nina winters and many of the other winters that were noticeably mild (but with periods of decent snow) often had a significant El Nino. This is not to say that winter can't defy this logic, the weather always seems to defy any logic but the probabilities weightings of cold verses warm can certainly be adjusted. It was also found that neutral winters tended to be drier across New England. The signal was not extraordinary but the stormiest winter seasons have tended to occur during significant ENSO winters on either side.

Our next point of focus is the PDO or Pacific Decadal Oscillation. We have defined it a few times in our many pre-season outlooks as an index which reflects the configuration of sea surface temperatures in the mid-latitude Pacific as opposed to the equatorial Pacific (where ENSO is decided). Like the SCWB, which also has become decadal, the PDO tends to prefer a positive or negative index every 15-20 years and thus the "decadal". Sometime around the birth of the SCWB the PDO turned negative and only two of the last 10 winters have had a positive index. There is a relationship the PDO has with the ENSO. Most La Nina winters feature a negative PDO and vice versa for El Nino winters. Since the relationship is far from perfect, the PDO does deserve its own little section in our pre-season synopsis. Like, the previous 3 winters, the PDO this year has a negative sign (-0.86 as of the last update) and this typically means weather patterns rotate in and out frequently. We have had and will continue to have an occasional encounter with the "evil empire". This term described the tightening of the jet stream in the Pacific caused by the clash of an upper level ridge in the Pacific and a trough over Alaska. The "variability" aspect of the weather in negative PDO years has been very evident during this year especially even through the summer. The weather since late last winter has been incredibly "normal". A few weeks of anomalous warmth has been followed by a few weeks of anomalous cold with each period failing to persist for more than 2-3 weeks. The shift to this elongated state of "normal" occurred after the first half of winter this year after the historic warmth of 2012. I suspect we will see more of this through the upcoming winter though I think there is reason to think that cold weather will win some important battles this year and further limit damaging thaws (though I suspect we will see them).

The source of some of the excitement and perhaps one cause of how the current month has "defied expectations" is the expansion of snow and ice in the northern hemisphere. The arctic actually saw a more abbreviated retreat of ice in the arctic regions verses the last few years (although it was still well below the 30 year average). The expansion through October and into November has been, shall I say, awesome. Once the final numbers for November are tallied, the October/November snow and ice cover in our hemisphere will rival the 2nd highest total in 40 years of recorded data. We only trail the bicentennial winter of 1976-1977, a winter that will long be remembered for  long stretches of historic cold. The Hudson Bay in particular is about 20 percent iced over as of November 21st, which would be the largest show of ice this early in about 10 years. It is my belief that the expansion of ice and snow is an important early season feedback. A larger area of snow and ice cover creates a larger breeding ground for arctic cold and it is arctic cold and often the strength of this arctic cold that can often times make or break a winter. We have seen an early taste of exactly that early this season with continuous invasions of arctic chill even when some of the teleconnection indices have argued against it.

So what do we make of all this ? We can finally forecast a cold winter !!! I have not done that too much since it typically is a bad bet (though I have forecasted a few snowy winters). The colder than average temperatures will result from what I think will be a few nasty periods of bitterly cold temperatures but the aforementioned PDO will still allow for some variability and the occasional thaw, even a damaging one. The neutrality of the ENSO would suggest less in the way of storminess so I am reluctant to sell my soul to a snowy winter. We should see at least something in the range of normal. For the record I will say 1-3 degrees below normal on temperatures and 260-280 inches of snow (which is just to the above side of normal). Get your mad cards and get your ski's ready, I expect a fun winter !!