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Wednesday, January 9, 2013

Thaw still expected Sunday/Monday and some icing possible next week

The mountain has been hanging in there pretty good so far. The arctic cold has receded and Pacific air is largely encompassing New England. As of now, the effects of this have been minimal thanks to the deep snow, low sun angle and so far light winds. The latter of these will be the most critical in the coming days. So long as we keep the wind down, the relative warmth that has invaded the middle layers of troposphere will be unable to mix to the earth's surface. Winds will increase during the day Wednesday as an upper air disturbance and area of low pressure centered well to the region's north approach. Temperatures may creep above freezing again but snow showers will commence late in the day as the instability increases. I would expect maybe an inch or two from this followed by a dry and somewhat sunny day Thursday with diminishing winds and temperatures again near or just above the freezing mark.

The wind issue will become even more critical as the weekend approaches. Understand that the upper ridge along the east coast is mammoth in nature, easily supporting record breaking warmth in areas where the lower troposphere is well mixed (windy). Areas that are cloudy with light winds can avoid this fate. Much of Vermont will successfully do this Friday as clouds cover the state with temperatures still in the 20's and 30's. Precipitation from a decaying wave of low pressure will arrive later in the day and although temperatures will in many areas be above freezing by then, some areas could see some freezing rain. Most of this will be over with by Saturday morning except perhaps for some drizzle. I think Saturday's potential warmth could also be thwarted by clouds, of the low clouds or fog variety which would mean another day with temperatures in the 30's. Some sun on Saturday could push temps into the 40's however.

Sunday and Monday is when it could get real ugly. Higher winds, higher dewpoints, a period of rain and an extended period of above freezing temperatures will do damage to our snow. Arctic cold is expected to seep back into the region slowly beginning Monday but hardly in decisive fashion. The colder air will actually be undercutting the very persistent and still very potent east coast upper ridge. This undercutting will set the stage for a dramatic temperature gradient stretching from the Ohio Valley into New England. Waves of low pressure along this boundary, one or perhaps two of them could impact the region with precipitation. This is a battle where the cold air seems mostly out-gunned but there might be enough available to set the stage for an extended icing event next week. Arctic cold undercutting large east coast ridges does happen now and again in New England and some big ice storms have been the result. The one that comes to mind is early January of 1998 where (if I can remember correctly) members of the MRG coop volunteered to clean out all the tree damage from our beloved gladed terrain.

Eventually the east coast ridge will get pushed out and it will happen quite abruptly with some very strong Arctic chill possible for the weekend of the 19th and 20th. Ensembles have diverged a bit on the overall "favorability" of the pattern but I continue to think that the negative NAO will win the day, producing an extended stretch of rain-free weather and below freezing temperatures.

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