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Sunday, December 23, 2018

Not much new snow to promise in the short term but pattern looks better as we move toward 2019

After getting roughed up pretty good on Friday, we are obviously anxious for immediate relief and I can't promise much in the short term; in fact, we have another less than desirable set up late in the holiday week which we can detail a bit more today. That said, the jet in the Pacific will gradually weaken over the next two weeks, the PNA is expected to build and the outlook for the early part of 2019 looks colder and potentially snowy as well.

We do have a weaker weather system that has consolidated a small amount of moisture but has done mostly south of Vermont on Christmas Eve. As a result, the mountain won't see a lot of snow on Monday, just some flurries or a brief period of lighter snow which will amount to a coating or up to an inch. Those flurries will continue into the evening before conditions dry out and skies clear and allow for some limited sun on Christmas Day with temperatures starting out around 10 and rising into the 20's. An even weaker impulse will pass Wednesday but moisture is so limited that I would not hold out hope for much. It will remain below freezing Wednesday and that will continue through Thursday, a day which should feature more sun and some terrific visibility and relatively calm winds.

The Friday-Saturday situation has been and continues to be watched quite closely. If we are to salvage anything truly special out of this holiday stretch, it has to happen with this storm on the 28th or 29th. Unfortunately, we are still dealing with the by-products of an adverse pattern and a storm that will mature in the central Rockies and become a excellent snow producer for much much of the ski areas both in Colorado and New Mexico. With the storm reaching maturation in the central plains, some serious hurdles exist and another big warm push of air will make its way up the eastern seaboard. The situation however is not as trying as this past Friday. If one takes the consensus of available data, the track of the storm would be just north of the Canadian border and I've seen some simulations where the mild air fails in its efforts to reach the central and northern Green Mountains. There have been other simulations that have temperatures soaring well into the 40's again. In either case, I would expect a period of mixed precipitation early Friday with temperatures approaching the freezing mark and a possible period of rain later in the day if temperatures do indeed make that jump. This isn't etched in stone however, while last Friday's event more or less was by this point in time. Certainly worth checking back in a few days for an update.

In addition this weather situation evolves into Saturday as the front associated with this storm sags south, cold air reasserts itself across the state and rain potentially changes to a period of snow if a wave of low pressure along this boundary allows for such an extended period of precipitation. It is also possible that with the southward advance of what appears to be very chilly air Saturday, conditions simply dry out and precipitation is simply pushed too far south. Either way, I expect the drop in temperatures Saturday to mark the start of another extended period of sub-freezing temperatures and an opportunity to rebuild our damaged snowpack.

There has been lots of talk within the weather community and even in the media of looming and potentially historic arctic chill for January. The catalyst for such discussion is something called "Sudden Stratospheric Warming" or "SSW", a phenomenon which sometimes foreshadows extended periods of high latitude blocking in the jet stream and cold weather in lower North America.  Dr Amy Butler out in Boulder who works at CIRES is a terrific follow on twitter @DrAHButler  also has a blogspot page dedicated to SSW - Amy Butler's SSW Page, a phenomenon that has only gained attention within the last decade. Now, though a seemingly significant SSW is expected, it does not always lead to historic outbreaks of cold or even any outbreak of cold. Weather is very chaotic and historic weather requires a combination of factors to align in a specific way. From my vantage point, there is no evidence of historic cold but certainly a better looking pattern to start off 2019. This includes a softer Pacific jet and a positive PNA pattern capable of delivering a continuation of sub-freezing temperatures and most importantly an optimal storm track. I would thus expect 1-2 opportunities for snow New Years week, but can't promise anything big quite yet.


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