Northern Green's now sit on very western edge of accumulating snow for weekend storm

As promised, we should be able to provide a more definitive outlook regarding the storm this weekend. There has been quite a bit of noise regarding the upcoming weather situation and a lot of it seems to stem from a more recent phenomenon on twitter which involves selectively posting maps of models showing the snowiest of all scenarios.  The big reason I punted on an update yesterday was that models failed to provide anything truly conclusive in terms of a storm track and there never was a consensus for a 2-3 foot powder producing bonanza though twitter might have you believe that there was. Operational model data can inherently be statistically noisy and that noise is amplified when a 100 mile difference in the track of a storm changes the total snowfall by upwards of 2 feet. 

As of early afternoon Thursday, the data has finally converged on the idea of a big storm this weekend tracking close to the Cape and Islands. This storm, originating as an unusually strong southern streamer (given the La Nina) will indeed phase with northern stream kicker and deepen dramatically as many storms do upon interacting with the natural baroclincity of the eastern seaboard. The data today is in much closer agreement that the track of this storm stays mostly offshore. This is good for ensuring all snow but bad for total precipitation amounts and will thus keep a ceiling on total snowfall amounts for all of the Green Mountains. Much as I wished it not so, this was a trend I feared would continue Wednesday and we now sit on the western edge of the conveyor of decent snowfall with the good news being that the Vermont high country is one of the few locations that should see a powdery consistency to any snow. 

Only a minimal amount of cold air to work with during this event and following a relatively mild day Friday, temperatures are likely to climb into the lower or middle 30's in Vermont as snow begins during the early afternoon. As the storm continues to deepen near Cape Cod, temperatures will drop off into the 20s, especially across the high country but total snowfall will depend on whether we can pull this storm into Cape Cod Bay (even just a little). Should we be able to do this, our storm total could exceed 6 inches but should we not than it's a 2-6 inch wind-blown event with flurries and snow showers continuing into early Sunday. This is still an impressive storm and appears to be another knuckleball type situation for forecasters meaning another sudden change would not surprise me. 

The onset of the snow Saturday should also begin a healthy stretch of early December sub-freezing temperatures. Nothing especially noteworthy but readings should drop into the teens Sunday, Monday and Tuesday nights across the high country and generally stay sub-30 during the subsequent days. Our next chance for precipitation comes thanks to a milder push of temperatures during the middle of the week. It is a little uncertain how far northeastward this mild air, originating in the plains can push, but I am looking at some newer data suggesting it will not quite reach Vermont (at least not next week). One and maybe two impulses riding along this temperature boundary will bring the potential for some snow to ski country with the first arriving Wednesday and second prior to the weekend of December 12th/13th. 

Following what looks to be a rather tame weekend (December 12th/13th), we should see a bit more arctic air enter the forecast picture. The major ensembles are starting to show a weather system that may or may not get hung up across the southwestern U.S. after December 14th and this would certainly have an impact on the southward push of any arctic cold. Consistent with the last update however, Canada is expected to be a lot colder thanks to a broad area of ridging in Scandinavia and a slightly negative Arctic Oscillation. I I think this should ensure a period of below normal temperatures between the 15th and 17th of the month. The Pacific Ocean has shown a reluctance to cooperate however and I am skeptical and even doubtful that the stretch of cold 2 weeks out is the beginning of a more sustained period of below normal temperatures. Still, its not a bad two weeks but it would be a lot better were we to squeeze a decent event out of this weekend and we appear to be right on the edge.