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Sunday, December 1, 2013

Variable pattern to dominate first half of December

The big finale to November has many giddy about the upcoming month and why not, it has been a momentous week to ten days. In reality though, the first half of December is typically erratic and more recently a big struggle. This one appears that it will conform to this norm since in spite of some promising looking possibilities in isolated parts of the forecast period, the next two weeks as a whole is fraught with trouble.

Arctic cold still, as we speak, encompasses much of Canada and is helping to rapidly freeze the Hudson Bay (now ~ 60 percent frozen). Unfortunately, it's influence has someone subsided across New England and points south. Were it to be more pronounced, a developing coastal system Tuesday might have had a greater chance of manifesting itself into something significant. As it is, the system will develop and it will mainly be a mixed rain and snow producer for coastal New England, exiting the region Tuesday evening. The duration of the week will generally be free of any new snow. Arctic cold and snow will descend on the Rocky Mountain region while the east coast will see a warming trend. Precipitation, if it falls at all, will be rain Thursday night (although nothing more than a period of a few hours).

Speaking fundamentally, the pattern in front of us is being anchored by a strong blocking ridge in the Bering Sea. Blocking, in general is a positive thing and the jet stream in the Pacific will be "loose" as opposed to "tight" which is also a positive thing. Longitudinally speaking however, the Bering Sea blocking ridge still presents some problems since it is a mechanism for focusing cold on the western half of North America while there is no mechanism to hold the cold in place over New England or eastern North America. The result is a highly variable pattern with intrusions of cold, some significant followed by quick warm-ups. New snow, maybe even a significant snow is possible as well but a thaw might quickly follow.

After a day or two of above freezing temperatures later this week, there will the first move toward colder temperatures by the weekend but this turn to colder weather does not look like it will accompanied by any snow. The next best chance for good snow comes around the 9th or 10th of the month as a potential system exits the Rocky Mountain and gets catapulted northeastward toward the eastern Great Lakes by another big jet amplification across the west. Actually, the track of this system is still very much in question and if the amplification across the west is a bit more imperfect, it might generate a flatter system. The snowiest solution would probably involve some compromise of the above solutions. The potential storm (or no storm) will be followed by a more significant chunk of cold for the middle of the week but this to will be short-lived. By the 13th of the month there is some strong evidence to suggest a more significant push of warmer temperatures, perhaps even a significant thaw since the Bering Sea ridge may in face bottle up much of the cold in western Canada or at least that is what some of the ensembles are indicating.

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