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Wednesday, December 19, 2012

After some rain Friday, snow for the weekend and maybe some more next week

The mountains hung in there Tuesday and in the end really didn't see too much rain. With the additional snows Tuesday night, Mad River Glen is dare I say, a winter wonderland just without the skiers. Attention now shifts to the big storm set to brings its bag of goodies by Friday morning. I have some good news to report with this system but just as they like to say "all politics is local", all news is also relative. I set the bar pretty low with last night's update so lets see if we can raise it a bit.

This very powerful storm system will get pretty wound up across the Midwest Thursday bringing heavy snow, gales, and even severe thunderstorms as far north as the Ohio Valley. The storms early and very deep amplification does not bode well for interior New England and as has been mentioned already, warm marine air from out over the Atlantic will flood the region Friday morning. If precipitation starts as snow late Thursday night, it will go over to rain Friday and we could even hear thunder once or twice. So where is the good news you ask ? We can't do much about the slice of warm Atlantic air but models do show this storm evolving very quickly and thus occluding very quickly. By late afternoon Friday or into the evening, colder temperatures will gradually become re-established over the mountain and we should see a quick change over to snow. In the end, the rain and above freezing temperatures will probably persist for roughly 6 hours. A swirling occluded system, such as this, will make the storm appear like a poor man's hurricane by Friday night on satellite imagery and the center of circulation will gradually make its way into the Gulf of Maine by Sunday. The slow movement and instability associated with this storm should allow for occasional snow between Friday night and Sunday morning. Snowfall could be significant before its over, perhaps upwards of a foot or more across the upper half of the mountain.

There is another storm system that should garner plenty of discussion. For one, it could be very significant. Secondly, the likely time-frame is right after Christmas, traditionally one of the most popular times to make a few or several turns. By Christmas Eve, polar air, of a weaker intensity will cover a broad area of both the Upper Midwest and New England. Meanwhile the next in this continuing series of storms will organize in the southern plains, gather moisture from the Gulf of Mexico and proceed northeast around Christmas day. This system will have more cold air to work with than the preceding few storms but questions and uncertainty remain. The main concern involves another potential premature amplification across the center of the country. Would this happen the result could include precipitation other than snow. Other questions regarding the organization, timing and track of this feature could also hold a lot of sway on the eventual forecast. I am cautiously optimistic, but its early so lets just see how things play out.

There are conflicting indications as we heard toward 2013. There are indications that the evil ridge in the west-central Pacific migrates back to the east and starts creating more mischief. Both major ensemble packages do suggest a trend back toward warmer temperatures just prior to the New Year. At the same time, a succession of recent European Ensemble runs have trended toward a negative AO just before the New Year and have also allowed some of that ridging to extend into the Yukon in northwest Canada. If we can keep the ridge axis in the Pacific west of Hawaii and finally get some ridging in western Canada, it would produce a very ideal split flow scenario full of storminess and Arctic chill. Lets end the discussion on that and hope for the best


1 comment:

Misha said...

Excellent stuff. I'm still hoping for that Arctic chill, but hearing mixed reports for the region today, still sounding mostly wet. Fingers crossed that it starts dropping soon.