An upper-level low will develop and slide over the great lakes Saturday night and will move over New York and New England Sunday and Sunday night. It will be weakening as it moves over New England. This will spread snow showers and light snow to the area dumping up to 3 inches of snow to wake up too Monday morning mainly in western and central southern New England. At the same an upper-level low will slide down from southeast Canada and will push down into Maine creating possible ocean effect snow showers for parts of the coast mainly the outer cape.
Now you probably have heard chatter about a possible good size winter storm in the long range forecasts. The opportunity is certainly there. We will have a better handle of this system possible impacts to the Northeast Monday and Tuesday when all the pieces are over North America.
Current thoughts. Currently I am throwing out the GFS weather model even its ensembles been trash since its update, I just do not trust it. The forecast for this system of course is complicated. When is it not. The placement and strength of high pressure in canada, to the amount of cold air available to how strong is the surface low over the plains under the upper level low in the plains and timing of the transfer of energy from the parent low to the secondary low off the mid-Atlantic coast will all impact what this system brings to the I95 corridor and others in the Northeast.
Above is just one possible outcome for this storm system by EURO weather model Not a forecast but close to what I think may happen based on ensembles. Upper level low goes from central plains to northern plains and then pushed southeast into the Ohio River Valley and Mid-Atlantic. You see some 500v energy pushing through southeast Thursday/Friday, that is the kick starter of the coastal surface low, eventually the upper level low catches up to the surface low off the Mid-Atlantic/Northeast Coast as that energy swings out to sea.
A strong pacific coastal storm and associated upper-level low will spread rain and snow from southern British Colombia to central California. Rain showers and snow can make it all the way down to southern California and desert southwest. A surface low will redevelop under the upper level low over the central plains and looks to kind of stall over the northern plains Wednesday/Thursday as an area of high pressure over southern Canada blocks it from moving north. As the upper-level low moves east/southeast energy will start to converge in the southeast spreading rain showers and thunderstorms with a possible coastal storm developing off the Mid-Atlantic coast Thursday and Friday on the southeast edge of the upper-level low which will still be centered over the Ohio River Valley.
Eventually the upper-level low will reach the mid-atlantic coast Friday night and the original coastal surface low somewhere south of New England could realigned closer to the center of the upper level low, it then based on current guidance we could see it strengthen and we may have a (all southern new England snow lovers 5 favorite words) nor-easter going through the Benchmark. If current thoughts are on the right track, this would be a long duration event. More details to come.
Long range, an active pattern continues, and we could have one of the best winter patterns in December we have not seen in a long time in December. Dare I say it, the odds of a white and cold Christmas is elevated for many.
Merrimack Valley Weather 