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Sunday, November 28, 2010

Big block over Greenland will ensure cold and some snow after Dec 1

A large upper air "block" has certainly established itself across Greenland over the past week. It has tag teamed with another high latitude blocking feature centered over the Bering Sea to allow arctic air to flood the country and will ensure a generally favorable early season pattern for the beginning of December. The benefits of the negative NAO will unfortunately not be felt until after the 2nd or 3rd of the month. The Bering Sea block has allowed a large trough to form across the inter-mountain west and this in turn will allow a large fetch of mild southerly to flow to establish itself across the east and this will flood the region with mild air very quickly on Tuesday. The rain will soon follow and rain it will to the tune of 1-2 inches. We might as well get this out of the way now because an event like this would have a devastating impact on skiing were it to come prior to the Christmas holiday.

So speaking from the standpoint of the MRG "base" we will be starting from scratch on December 2nd but a sustained period of cold weather will begin on that day. Temperatures will be seasonable through the upcoming weekend and by the looks of it, we will not have the instability for a big terrain induced snow event. There will be a lingering "baraclinic" area (you could say front) in the Gulf of Maine and this has the chance to stir up a bit of snow though the chances for accumulations will be best over coastal regions though much is left to be determined. The combination of better instability and even weak weather systems should result in some new snow early next week and hopefully by then we can start discussing a opening day party.

There is evidence that the block over Greenland will begin to break down around December 10th but our Bering Sea blocking feature will remain. The pattern will thus turn more variable but we should begin to churn out a few weather systems as we approach the middle of the month. There are a few additions or side features which should help to provide more of a numerical summary. Included will be seasonanal and 7-day snowfall totals at MRG and expected snowfall over the upcoming 7-day period. I will also include a favorability index. This will be a very generic, cumulative measure of the three teleconnection indices: the Arctic Oscillation (AO) the North Atlantic Oscillation (NAO) and Pacific-North American (PNA index. The AO and NAO index is favorable when negative while the PNA is favorable when positive. Thus for the purposes of the "favorability index", the signs of the AO and NAO will be flipped and added to the PNA index for a final total. This approach has weaknesses but it will be a simple non-subjective and numerical way of looking at the next two weeks since our newly devised "FI" will be calculated at 7 and 14 days.

1 comment:

Tommy said...

Thank you Josh, as an aspiring leader of our self proclaimed, local team of "Ski Guru's", your information is vitale to stifle those who choose not to head my weather knowledge. Can abody enlighten me as to how the new Favorabilty Idex will read, such as a scale or schedule as to what would be considered bad, good or great?