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Saturday, December 1, 2012

Competing forces battle for control of Vermont's weather after the eary month thaw

After a nibble of the white stuff and a bigger taste of some single digit temperatures, the mountain will be forced to endure a significant stretch of above freezing temperatures and some rain. All of this has been in the cards for some time so there is nothing too surprising or alarming. All of the big questions and potential concerns relate to the period beyond Thursday. There are reasons to be optimistic but there are also reasons to be nervous. The weather pattern confronting the region involves many competing variables and which ever one wins the day will largely determine whether or not the mountain can be set up with an early opening.

It's not worth spending significant amounts of time on what amounts to a meaningless thaw. Temperatures should surge into the 50's Tuesday and the combination of mild weather and rain Tuesday night should essentially wipe out most of the snow below 3,000 feet.

More seasonable temperatures and even a bit of terrain-induced snow should prevail later in the week which is where much of the uncertainty exists in our forecast timeline. As mentioned there are competing features on our playing field. The big concern, at least from my vantage point, is that the medium range ensembles are showing the return of the dreaded upper ridge in the east-central Pacific. My personal loathing for this feature has been on full display for well over a year now and my reaction is a mix of both dismay and skepticism. The preseason prognostication mentioned that the ridging in the mid-latitude Pacific has really not been an issue this fall and the disappearance of La Nina certainly discourages its development this year, at least for an extended period of time. Yes, it still could prove to be another tease, but we have to be honest, such a feature works to tighten the jet in the pacific, encourage zonal flow, and all but eliminate the ability of cold air to sustain its coverage of mid-latitude geography over the eastern United States.

There is a brighter side of this possibility spectrum so I hope I have not completely killed the mood. The hemispheric picture consists of much more than a east-central Pacific ridge. In fact, there is clear evidence of ridging in the Jet Stream extending from the Aleutian Islands northward over the north pole and southward to Greenland and the Davis Strait. Essentially, the ridging forms a ring-around-the-rosie encompassing an area of very cold air across Alaska and western and central Canada. The cold has allowed for a rapid expansion of snow and ice across North America as a whole and most importantly for us, the Hudson Bay. Look at the coverage of ice on the Hudson Bay this year compared to the last 5.

2012 -

2011 -

2010 -

2009 -

2008 -

The freezing of this large body of water, and freezing it early is monumental in getting a good build up of cold over eastern Canada so it ultimately can become an asset in our crucial winter weather scenarios.

Cold weather across Canada is not the only reason to be optimistic. The two major ensemble packages largely disagree with one another on how this all plays out by next weekend. The American GFS package depicts a scenario that hinges on the aforementioned Pacific feature. Two additional and significant surges of milder weather are likely in such a pattern which would be dominated by a negative PNA and more minimal high-latitude blocking. The European package paints a much more optimistic evolution which would have cold weather returning by the end of next weekend and remaining in place for an extended period there after. This set-up hinges more on what is indicated to be a negative AO and a broader extended reach of the bitter chill across Canada. Most interestingly, the European also depicts the potential for our first major snow producer around the 10th of the month. We have not seen evidence of such a storm until today we would love to see it.

I thought it was interesting to see how similar this year is matching 1984-1985. November of 1984 was a touch below normal on the east coast (same as this year) but more significantly below across western Canada, much like this year. The December that followed featured cold weather across the U.S. and mild weather covering much of the east coast, much like the GFS ensemble depicts. The ensuing January was then bitterly cold featuring the coldest Presidential Inauguration ever recorded when Ronald Reagan was sworn in for his second term. I am closely watching how this plays out, and whether we continue to follow the 1984 scenario in accordance with the American ensemble or whether we diverge like the European suggests.


VCS Student Senate-Run Blog said...

Fingers crossed for snow on the 10th! Thanks for the post!

jonathan perillo said...

I thoroughly enjoy reading your posts. You have become a shortcut icon on the home screen of my phone. Keep up the good work! And let it snow!

jonathan perillo said...

I thoroughly enjoy reading your posts. You have become a shortcut icon on the home screen of my phone. Keep up the good work! And let it snow!

Abubob said...

Very interesting analysis. It lends credence to my own personal (and humble) theory that this winter will be a "building" winter. Much like 06-07 was after the dismal 05-06 winter. The successive winters building until 09-10 then declining in 10-11 and (hopefully) bottoming out in 11-12. So maybe a slow start this season finishing with a bang? Then next season even better? Time will tell.

VCS Student Senate-Run Blog said...
This comment has been removed by the author.
Gabe said...

What's the status on the upcoming storm?? Let's hear more!