Think Snow, Tweet Snow !!!

Sunday, February 17, 2013

3-6 inches of snow Tuesday night and "hopefully" more during the upcoming weekend

At the jet stream level over the next week, the two big prevailing features on the weather map are a blocking ridge across the Hudson Strait and the broad ridge in the mid-latitude Pacific which we have appropriately named "the evil empire". We saw this general set up in the last half of December and active pattern was the result then and we are expecting an active pattern this go round. "The evil empire" which consists of a tightened Pacific Jet Stream can produce some powerful systems but also act to force a northward retreat of Arctic cold. Both of these byproducts will be on display over the next 10 days which should feature moderating temperatures but talk of precipitation, hopefully mostly in the form of snow.

One of the issues going back into December was the early maturation of some of these healthy looking Pacific storm systems. As a result, the mountain often got a weakened version of these once vigorous systems or dealt with problems relating to a lack of cold air. Still, the period stretching from mid-December through new years was the snowiest period of the year and we would take a similar result this time. The first storm system in what should be an extended series of storms will peak in the Great Lakes, occlude and then spin into the St Lawrence Valley. The occlusion will halt the warm push of air and allow the relatively brief period of precipitation Tuesday night into early Wednesday to be snow. This will not be a healthy system when it arrives and snowfall accumulations will be in the 3-6 inch range. It is enough to produce a bit of a powder day Wednesday ? Yes !

I still have high hopes for the 2nd system which will be a big snow producer in the 4 corners region but like its predecessor, will reach its maturation too early. Yes there is a dirty R-rated analogy that I could use here but this is a family friendly blog and I thus stick to the baseball or football analogies. The occlusion, which will again occur over the Midwest is essentially the end of the strengthening phase and as the storm pushes east, its area of moisture and precipitation will slowly decay. What can reverse this process is the development of a coastal low on Friday or Saturday of the upcoming week. This will produce an enhanced area of precipitation that would raise the potential for a healthy accumulation of snow for the upcoming weekend. I hope this occurs but to be perfectly candid, recent model guidance has not been particularly bullish on big snow from this storm, at least right now, although there is plenty of time for models to change their tune.

The active pattern will indeed produce at least a three-part series or trilogy of systems. The third strikes around the 26th or 27th of February. We will face the same challenges with this system including early maturation over the Midwest and potentially even a lack of cold air. The Hudson Strait blocking ridge is thus a critical part of the puzzle. Ideally, a feature like this prevents weather systems from invading the eastern provinces of Canada. We need to get another such assist; otherwise, we could be dealing with a precipitation producer other than snow. There are indications of potentially one more system prior to or during the first full weekend in March. At this point, the jet in the Pacific is expected to weaken which could allow for some colder temperatures to get into the mix.


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