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Monday, January 21, 2019

Surge of milder temperatures Wednesday will only slightly interrupt what is a cold and snowy setup for end of January

Just like the New England Patriots football season, there was a time in late December where things seemed to be unraveling just a bit. And as the Pats advanced to yet another Super Bowl, Mad River Glen was procuring another storm of close to 20-inches and is further cementing the winter season as a truly memorable one. Though we are certainly on a pace to do just that we have to keep this train rolling.

Directly ahead of us remains a complicated forecast picture and an unfortunate push of mild air. Often times, computer forecast simulations fail to pick up on a overrunning surface until within a day or two of an upcoming event. I have been holding out hope that some of the bitterly cold temperatures that have gripped New England will continue to do so through Wednesday/Thursday of this week but indications are that this air will get mostly flushed out at varying degrees. As of late Monday, there remains some disagreement regarding the extent of the mild intrusion but the tepid consensus is for some light snow to develop on Wednesday and give way to a bit of freezing rain and then rain during the overnight hours. Though temperatures could make a run at 40 by very early Thursday this won't be a significant thaw and as moisture continues to stream up from the south on Thursday, a wave of low pressure could potentially change the precipitation back to snow for a time before the event culminates Thursday evening.  Stay tuned to the forecast because last minute changes are likely.

Modestly colder air will work its way back into the region Friday and a clipper system marking the advance of bitterly cold temperatures should spread snow showers into the state as the day progresses. The snow does have some accumulation potential. Meanwhile, there has been lots of talk regarding the incoming attack of the "Polar Vortex" and the first such approach will come Saturday though it appears as if we simply get a glancing blow (The PV will only make it just south of the Hudson Bay). Colder temperatures will advance into the Vermont high country late Friday and Saturday will be quite cold with a sub-zero low and a high of only near 10 but this is about 10 warmer than MLK Monday.

Temperatures are actually expected to moderate modestly by the end of the weekend and all eyes will be on a major amplification that is expected in the jet stream for early in the week. It looked for a time that it would simply be a peak in the arctic insurgency but it appears as it the action in the jet stream is associated with what could be a major league southern streamer. With the polar jet on the playing field, it sets up a highly dynamic situation involving the presence of arctic air, big time moisture associated with a strengthening low pressure center in the gulf states and a potentially big and phased system early next week moving up the east coast.  Some big snow is certainly possible and if we don't get it that way, we could certainly get it from a succession of polar jet disturbance with one arriving Sunday and another marking the advance of more bone chilling arctic cold around the time frame of Tuesday/Wednesday (Jan 29-30). So much could happen, and like I said in the last update, most of it good !

We then advance the calendar toward February and we will have a few things at work. Continued blocking in the jet stream and a negative Arctic Oscillation will keep arctic air at least close by but the most intense blocking is indicated to shift northwestward and thus may allow the focus of the most intense arctic cold to shift more toward western North America. This should help keep the region more out of the way of some of the more bitterly cold arctic air. That said, the jet stream in the Pacific is not indicated to intensify so it would surprise me to see the polar grip entirely capitulate. There is also no reason  not to believe in the magic of this modest El Nino which should continue to support a healthy southern branch of the jet and thus keep the storminess in play.

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