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Tuesday, January 30, 2007

New snow for the weekend more cold for next week

The contents of the last post included a prognostication of what the contents of this post would be; specifically, talk of significant new snow in the days ahead. Indeed there is much to talk about in that regard. The recent cold weather has moved January of '07 well ahead of January '06 in terms of skiing quality but new snow remains in high demand. Using the Mt Mansfield snow depth graph as a reference (since it is readily available on the web at http://www.uvm.edu/skivt-l/?Page=depths.php ) there is certainly evidence of significant gains during the last two weeks, but we remain over a foot below average and in a pattern like this I would certainly like to make up that ground and then some. Today's update is going to get lengthy with all of the goings ons since new snow will come at us in varying forms and varying times. There is also more very cold weather on the horizon which is poised to impact the western High Plains then Midwest and deep south perhaps in record breaking fashion. It will take a bit longer but this cold will eventually push into northern New England early next week.

Tuesday/Wednesday
Short term details could really bog us down on a day like this but to summarize, we will have to accept a wide-right on Tuesday's alberta clipper system which should bring a few inches to southern New England. A much weaker disturbance will bring light amounts of new snow to the northern Greens later Wednesday yielding the possibility of a few inches of the fresh stuff by Thursday morning.

Friday's Winter Storm
So this is how the board will get set on Thursday. The massive western ridge positioned near the B.C. coast which was hyped in the last post because of its amplitude will trigger a massive intrusion of arctic air which will make U.S. entry in Montana. Meanwhile, a southern branch system gathers moisture and awaits Polar Jet interaction. The result is alot of speculation, banter and all-out debate amongst eastern U.S. snow enthusiasts over what may go down late this week. The southern feature has a head start and indications are that it will move way out ahead of the arctic push and allow a storm to gather in force over dixie. What is more critical however is that the southern branch will ultimately get flattened by the strength of the pattern or the magnitude of the polar jet. My flight from Kansas City to Baltimore, MD Monday took less than two hours thanks largely to the strength of this jet. What this means essentially, is that although moisture will move up the Atlantic coast in impressive quantities (thanks mostly to that westward trough shift discussed in last Thursday's post), the failure of the southern branch impulse to perturb the polar jet will prevent this moisture from wrapping itself deep into interior sections of New York and New England for a long duration as the storm proceeds up the New England coast and thus prevent a huge Friday snowfall in central and northern Vermont. Forecasters look for a storm to attain what is called a "negative tilt" which indicates how much moisture will is thrusted west of the track With that said, I do think some of the deep moisture makes its way into Vermont for at least a shorter period of time allowing for what would amount to a few hours of moderate to heavy snow early Friday and an initial guess of 3-7 inches.

A complete upcoming weekend synopsis
A subsequent update refining these ideas will be needed of course but a as of now, a break in the snowfall is anticipated later Friday as an area of subsidence in the wake of the aformentioned non-negatively tilted storm moves through. As this is occurring the flow will gradually align itself vertically and allow terrain induced snow to develop across the entire chain of the Green Mountains either Friday afternoon or Friday Night. The snowfall could enhance for a time as the upper air impulse marking the advance of the very cold arctic air approaches. Terrain/Mountain induced precipitation is difficult to forecast both in duration and amounts this far in advance but the shear, stability and boundary layer moisture parameters will be met for at least a time (all part of the Braeton checklist !) prior to and during opening of the single Saturday morning. What does this all mean ? To summarize the guess is for two periods of snow, one early Friday and one early Saturday enough to produce a pair of powder days and an initial guess of 10-20 inches of snow for the period Thursday night through Sudnay. Wind will become a factor Saturday as will the cold weather. High temperatures Saturday will be in the low teens followed by a Sunday where temps fail to make it out of the single numbers.

Cold takes center stage
The big story for next week is the cold weather. In terms of both expansiveness and intensity, the attack of cold this weekend into early next week across the nation is as impressive as anything we have seen since December of 2000, perhaps dating back to 1996. It will make some headlines especially across the deep south. New England is one place which as seen its share of cold in more recent years and I refer mostly to January of 2004. Whether or not we can challenge some of those 2004 numbers which exceeded -20 in many areas remains to be seen but if it were to happen, Tuesday and Wednesday (February 6th and 7th) would be the time frame. Just prior to the peaking of the cold over the north country, we will be watching another system track near or just off the southeast coast. This system, a product of the southern branch may prove to create headlines either in the Mid-Atlantic or Southeast but it does not stand a chance against next week's overwhelming polar jet which will at some point, shunt this system out to sea before it plays any role in determing the weather at MRG. The polar jet will in fact ensure a fairly dry week for MRG overall with snowfall through the middle part of next week limited to the high terrain and falling in small increments.

Longer Range
As we move toward the weekend of February 10th, the ensembles do clearly suggest a relaxing of the polar jet. Even as this is occurring the Arctic Oscillation will remain at its lowest levels of the winter (-1) which will suggest that Arctic air will remain on the playing field in some fashion. This type of evolution, if viewed optimistically, would be interpreted as a chance to get some of the southern branch's deep moisture in the form of a well developed storm system up this far north. Pessimestically speaking, if the longwave trough/ridge structure were to align in the worst possible way it would allow for the possibility of a rain event. The latter would not be my guess. Recall that our early winter struggles were largely forced by an AO of positive 4. If the AO were to maintain a negative state it will be difficult for low pressure centers to track north 50 N along the east coast, a track necessary to bring rain to MRG. I do think temperatures move from their much below status to slightly below in the period between the 10th and 14th of the month. It also seems reasonable to expect at least one snow event after the very cold but fairly dry period between February 6th and 10th.

The Quick Summary
Snow will fall for varying weekends between early Friday and the end of the weekend. This is followed by very cold weather next week and then closer to normal temperatures for the weeek beyond.

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