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Tuesday, December 13, 2011

Encouraging signs in some of the Ensemble data

Yet another round of mild weather and rain is poised to invade interior New England and specifically the northern Green Mountain chain. Temperatures will soar well into the 40's Thursday and we will have to endure a period of rain during the middle of the day. The weather system responsible for the rain will bring colder weather, much colder weather in its wake. We will finally start to benefit from the 80 percent frozen Hudson Bay and colder air will thus be able to access eastern Canada more freely and more vigorously and can push southward from there. Temperatures over the weekend will stay well below freezing through the weekend and a clipper system Sunday should spread a fluffy accumulation of powder to the mountains.

Our pivotal pre-holiday moment will come early next week, likely Tuesday, as the cold air relinquishes its grip on the region and a stronger storm system approaches from the southwest. There are questions about both the track of this system and the available cold air and I am certainly concerned about both. We have as you know, no blocking mechanism to keep cold air in place and the prevailing pattern and warm Great Lakes has constantly pulled these systems farther north and farther west. It is very possible if not likely that next Tuesday sees this very result. With all that said, models are still odds and have yet to settle on a solution and are allowing for the possibility of a more wintry scenario.

Tuesday is important because if we can get some snow or even sleet out of that system, the stage will get brighter. The European Ensemble which has been accurately predicting almost tropical weather for the northeast over the past 3-4 weeks is finally showing some key changes starting in the middle of next week. It is not total vindication but the pattern will get an important boost from at least the temporary establishment of a western North American upper ridge. This should send some rather impressive shots of cold deep into the U.S. as we approach Christmas. The polar vortex in Alaska will also weaken at this point allowing the Jet in the Pacific to relax. The pattern in the Pacific is still disconcerting. It will still feature a lot of this Jet Stream level warmth referred to as ridging. Last year the Pacific was surprisingly unstable at mid-latitudes and this was attributed to the highly negative AO which dominated the weather pattern for December and January. Going a little deeper into the world of "geek speak" meteorologists talk about the formation of a high latitude "block' as a stratospheric warming event. A sudden warming of the stratosphere signals the formation of a high latitude block and thus signals that there will be a major southward transport of arctic air somewhere. The stratosphere which has been very cold so far this winter is expected to see such an event in the next 7-10 days. The phenomenon can only be viewed in general terms and does not reveal specifics. All we know is that the atmosphere will get shaken up, at least a little as we get toward the holidays. Given what has happened so far, we have little too lose from such a shake-up.

1 comment:

ml242 said...

thanks for the update.