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Tuesday, February 3, 2015

A long and winding update full of optimism !

One of the crazier weeks of weather I have seen across New England as a whole and MRG has not been left out. We have been "bringin it" this winter and I think we will continue to do so through the remainder of this month and perhaps even through a good part of March. A lot of New England weather nuts are born out of week's of intrigue such as this and I have certainly done a lot of thinking as to how we got here (though I hardly have had the time to that since it's been so challenging keeping up with all the changes).

Our recent run of success and expected continued success is a result of many things, but two in particular that are noteworthy. The first we have discussed a few times already - The sea surface temperatures in the mid-latitude Pacific and PDO (The Pacific Decadal Oscillation). The PDO has soared to one of it's biggest positive indices in recorded history (which is a little over a century). One of the key drivers of this high index is an area of relative sea surface temperature warmth in the Pacific that hugs the west coast from the Gulf of Alaska south to the Pacific Northwest. This has made it especially difficult to break down any upper level ridge positioned in that particular region and even more difficult for any long wave trough to position itself there for any significant length of time. It all amounts to very good news on our side of the continent since a upper ridge over there usually means an upper trough over here. Most importantly, it substantially reduces the risk for a thaw, something we have not seen this past January for a change. The second is counter-intuitive but something I have spent some time thinking about the past week. Most east coast weather enthusiasts associate a "negative" NAO (North Atlantic Oscillation) with snow and cold and there are good reasons for this. During the heart of winter however, a negative AO and especially NAO combination can but a tremendous weight on the winter jet stream, suppressing the storm track and leaving northern New England high and dry. There is no doubt the traditional negative NAO is a productive variable for snow and cold in the Mid-Atlantic section of the east coast but I would hesitate to categorically say that regarding New England, particularly northern New England. Perhaps a different set of variable combinations and this would be true and if one is to remove a persistent western upper ridge in the jet stream and we are having a different conversation. In 2014-2015, the NAO has been persistently positive and is expected to continue to be positive. The storm track has not been forced southward even when models advertise such and the Mid-Atlantic has almost entirely missed out on all of the snow that has fallen on New England. This is one of the biggest reasons I removed the "favorability index" from the blog this year. The whole idea of "favorable" is difficult to quantify and the point is underscored with this seasons weather.

Moving back to the day-to-day, it's been a snowy time for us in VT but a cold time. We haven't seen too many days where the temperature has gotten past 10 in the last ten days. We should see more of this over the next 5 days or so ahead of moderating temperatures later next week. In the short term, a clipper system is going to try and grab ahold of some southern branch energy on Wednesday as it advances toward the east coast. A couple of runs of the European suggested that we might spin something up out of all this leading to more significant snowfall Thursday. Given the recent run of weather, one can't completely discount that possibility though models today have driven most of the action off shore. Still, very fluffy light snow beginning early Wednesday and ending early Thursday will amount to 3-6 inches and provide a nice topping to the 2 feet we have received over the last 10 days.

More very cold weather follows for Thursday into Thursday night including readings down near -15 Friday morning. By Saturday, temperatures bounce back into the teens as a weaker clipper approaches and brings some very light snow back to the region. Sunday is then very cold again as we get sent a direct shot of arctic chill out of Quebec.

The storm we are all watching now would occur in the early part of next week. The tangent I went on a few paragraphs ago might be apropos for this situation. A vigorous looking system is expected to drop out of British Columbia and amplify the entire pattern across eastern North America by Monday. The system will bring snow to the Midwest before attacking the Eastern Seaboard. The nature in which it does so is the question. Will the storm get suppressed as some of the models have indicated or can it get just a little kick from a receding polar jet and produce another round of fireworks across New England. Model consensus suggests more in the way of the suppression but it has not been a good year to bet on that so I would not count this storm out at all.

Temperatures are expected to finally moderate, perhaps even reaching above normal levels for a few days during the middle of next week. It won't last long however since the pattern will be unable to completely eliminate the western upper ridge and thus the pattern will revert back to a chilly one by President's day weekend. More snow is also possible around the time of the 13th-14th of the month as the pattern re-amplifies.

1 comment:

maxbuhac said...

This winter, it seems that whenever things look bleak, we get a nice surprise. Like the end of the super bowl.