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Thursday, February 20, 2014

Polar Vortex V poised to bring it next week after some minimal melt Friday and early Saturday

Most of the mountain will only see a brief window of rain on Friday and thus this will not be a particularly intense thaw or nearly as bad as the one we experienced back in mid-January. Precipitation could actually arrive as a serious burst of snow or a snow/sleet mixture before changing to freezing rain just before dawn. Ice accumulations could be significant as some of the heaviest precipitation will be occurring right around 7AM Friday with temperatures still expected to be a touch below freezing. Temperature cross sections suggest the icing will the most severe at the summits with very little opportunity for rain at any point in the day. Sometimes these situations become counter intuitive with the more protected valley locations getting the worst of the icing but in this case, the inversion in the atmosphere is shown to be well above the 4,000 feet. Temperatures in the lower sections of the mountain will creep above freezing Friday afternoon and thus the period of rain. All precipitation will end by Friday evening.

Saturday is expected to be a milder day and dry in the morning. Readings will be sub-freezing in the morning but rise well into the 30's by early afternoon thanks to some early day sunshine. Perhaps this is not a bad thing since it will give the snow an additional chance to soften and the water to soak through and run off. There are a couple of weak jet impulses that could bring snow back to the mountain as mentioned 2 days ago. The first arrives late in the day Saturday with snow showers arriving even as temperatures remain above freezing. The scenario is almost analogous to a summer afternoon thunderstorm since warming temperatures Saturday will turn the lower troposphere unstable and allow the development of some convective snow showers. If we are lucky, we could squeeze out a few inches out of a burst of snow. Flurries and lighter snow showers will continue through Sunday with temperatures remaining generally below freezing.

Polar vortex round 5 begins next week. The center of the deep freeze will actually stay in Canada, mostly over Ontario and Quebec but interior New England will be back in the deep freeze as well with temperatures well below zero during the mornings Wednesday through Friday and only in the teens during the afternoons. There are weak weather features early in the week that could bring light snow to the Green Mountains but none look substantial. The southern branch is not completely dead but it will be suppressed south much of next week and a weak area of low pressure is expected to be one product of that early Monday. This storm and its impacts area expected to remain well south of Vermont and the best we can do is probably another round of snow showers or a brief period of lighter snow/.  The next weak weather feature late Tuesday is more of a clipper and may bring a round of light snow to Vermont before bitterly cold temperatures advance into the state Wednesday.

The real active weather begins in March as the PV relaxes and recedes and another round of split flow in the eastern Pacific and western North America emerges. There are signs, even 12 days out, of a major storm in the time frame of March 3-5, the first of what could turn into another very productive period for powder. With much of this thaw mitigated, there is little doubt that we will move into March with a healthy base and additional snows will quickly turn conditions very good.