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Wednesday, April 22, 2015

MRG season ends but late April snows set to begin

The MRG season came to an appropriate finish this past week and weekend with a corn-fest. One might have intuitively expected that winter was finished given the several days of 60-degree weather we experienced but winter only just preparing for a late April encore performance. The show begins Wednesday night April 22 with rain at the very low elevations and snow above 2500 feet. The culprit for all this is an expanding upper level ridge encompassing most of central and western Canada. The remaining cold air at the poles will thus descend on the eastern two-thirds of the United States causing more than a week of unusual late April chill and in some locations, additional snows. Interestingly, the weak weather system responsible for the initial burst of rain and snow Wednesday night will strengthen, slow and ultimately get sucked west by a strengthening eastern U.S. upper trough. I think of these systems as “Maritime Stallers” since the storms travel to the Canadian Maritimes but then fail to make any additional eastward progress. The last several years have seen a scarcity of such events but they should be more common and are often very fruitful. They bring pockets of instability, moisture from Lake Champlain in addition to their own decaying areas of moisture to the Green Mountains and the slow moving nature of these weather systems can allow the results to “pile up” quite nicely.

Snow showers should impact even valley locations across Vermont later Thursday, Friday and into early Saturday. Some occasional dustings in the Valley should melt with sporadic sunshine. In the high country however, the snow will be more persistent fall occasionally quite hard. Between the snow Wednesday night and the additional snows late Thursday through early Saturday, accumulations in the highest locations could be well over a foot. The snow might be wet in nature late Wednesday but the airmass poised to invade Vermont is very chilly and the snowfall will be powdery above 2500 feet on Thursday and Friday.

Temperatures will moderate somewhat over the weekend as we watch a series of spring “cut-off” low pressure centers impact the eastern part of the nation. The first will entirely miss New England over the weekend and will bring a cold rainfall to the Mid-Atlantic. The 2nd next week might have a serious impact on the entire East Coast. There won’t be much cold air left by that point, but the storm could still bring some high elevations snows to the Green and White Mountains.

I am working on an end of season wrap-up that I wanted to keep separate from this update. Didn’t want readers to be looking at a late April update for the next 6 months.

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