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Wednesday, January 30, 2008

Friday system will bring some snow but mostly sleet to MRG

Wednesday's rain (and wind) falls in front of a very strong cold front which is moving swiftly eastward. The front marks the edge of what is a weakening but still very strong arctic airmass which caused temperatures to approach record levels in parts of the Canadian prairies over the past few mornings. The cold is advancing eastward fast enough to actually undercut the area of precipitation and thus the front becomes "anafrontal" in nature. This essentially means that rain on Wednesday morning will turn to a period of sleet/snow during the later in the day before ending. A small accumulation of new snow can be expected before first tracks time Thursday but the day itself will simply be dry and cold with temperatures in the teens.

Friday's nitty gritty
The weather map would have us believe some promising things about our Friday system. The storm will eject itself out of the southern Rockies and entrain some serious juice from the Gulf of Mexico before making the left turn and heading northeast. Unfortunately for us the storm will be moving more north than east and will reach the eastern Great Lakes by Friday evening. The existing cold will try and wedge itself over New England and this will work as an effective defense against the push of mild weather during much of the event. Above freezing temperatures will reach some critical areas aloft and will prevent the event from being of the all-snow variety. The details, as best as I can see them, are as follows. Precipitation will begin in the form of snow during the late morning or early afternoon Friday and could become heavy enough to accumulate a few inches before changing to sleet during the afternoon. I do think that the bulk of the precipitation from this system falls as sleet with temperatures holding in the upper 20's through the evening. As precipitation ends late Friday there may be a period of a few hours where temperatures climb to above freezing levels before the colder weather returns by Saturday morning. With the return of the colder weather comes a brief period of instability and some snow. The skiing on Saturday will obviously depend heavily on how much snow falls over the sleet prior to first tracks time. It does not look as if it will be a big accumulation but 4 inches (the high end of the possibility range) would go a long way to saving Saturday.

Some new snow is possible for Sunday but early next week is still ominous
The two big medium range computer models diverge from Sunday forward. There is some loose agreement on the grand scheme but it is the details which remain up for grabs. The European model on Sunday does suggest that we get an impact from a passing clipper system and possibly a few inches of powder while the American model says its flurries only. Models also disagree with the exact handling of early next week although both suggest a warm-up and yet another non-snow and possibly a rain event. Without getting too bogged down in details (because the model disagreement makes them messy) Monday appears to be the day least likely to get an impact from the non-snow precipitation while Tuesday and Wednesday look especially dicey. One of those days could in fact turn extremely mild.

Long Range
Loyal readers of the blog are aware of the value I place in the Arctic Oscillation and its impact on the weather not only at MRG but all across the United States. The Arctic Oscillation is the easiest index to predict and the simplest way to measure high latitude blocking in the jet stream. With that said, we are getting zero help as the index is expected oscillate around +1 for the next 14 days. Part of the AO equation and perhaps the worst part is the Pacific Ocean happenings and they include that mid-latitude ridge the high latitude troughiness and the fast and furious jet which will continue to pound the Pacific Northwest. We desperately need this to break down even partially and the best way we can get this to happen would be the formation of a block in one of the key regions of western Canada or Greenland. We can still score sporadic victories but we are looking for a few weeks and at this point we need to hope that begins by Valentines Day because the current pattern is now expected to continue until at least February 10th.

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