Tuesday, December 26, 2017

Snow potential diminishes over the next week as very cold/very dry air consumes Vermont

Still feeling some lingering frustration regarding the shortcomings of our recent Christmas storm. No it wasn't what we had hoped in a couple of different ways. First of all, it happens. Weather is inherently unpredictable and only  somewhat less so than it used to be. The element of surprise and the tangibility of that surprise is what keeps the science interesting. Secondly, worse things will happen, like getting totally shut out of a predicted storm or getting 6 Christmas thaws in a row. The trailing clipper system associated with the storm was a much drier storm than forecast models suggested. Locations across the Midwest did quite well but the system dried out as it progressed eastward and many areas didn't live up to expectations. The coastal system, developed and intensified mostly as anticipated but its area of precipitation was quite compact and only grazed the northern half of Vermont. The dry air behind the system was very evident and reduced the lingering snow shower activity to nearly nothing and thus we have been sitting high, dry and very cold.

A good old fashion Polar Vortex will smack the state twice over the next week and produce the most extended, most intense chill since February of 2015. My guess is that over 50 percent of our time over the next week will be spent below the "zero" threshold. Wednesday's high of approximately 5 degrees will be one of the warmer days. Most of Thursday and Friday will be sub-zero and low temperatures both mornings will range between -10 and -15. The effects of the winds will be the strongest Wednesday/Thursday and will subside Friday.

The incoming 2nd PV will be associated with a much larger jet amplification and we've been watching this for a while since it presented the opportunity for a sizable east coast system. That opportunity still exists but the PV looks strong enough and far enough south to suppress most of the action. Though I wouldn't eliminate the chances for snow entirely Saturday, I've seen enough of these situations to remain on the cynical and somewhat pessimistic side. PV's typically, though not always, crush snow chances in Vermont. Usually, there is too much jet energy aimed in the wrong direction to allow a storms impact to reach interior New England. In addition, the shallow and highly stable chill that's often associated with these weather situations puts a lid on the lake/terrain snow. So I'm thinking mostly dry this holiday weekend with some sunshine and occasional flurries. Blustery conditions will return and it will remain very cold with temperatures generally in the single numbers by day and sub-zero at night.

The effects of the cold wave will continue through the middle of next week and it should remain on the dry side thanks to the strong aforementioned dome of high pressure.  Changes in the Pacific in the form of jet stream tightening will shift the pattern and force arctic air into retreat mode by the 5th-7th of the month (the first full weekend in January). As of now, this "retreat" appears to be a partial one as opposed to a drastic one. Blocking at high latitudes is expected to disintegrate but indices won't stray too far from neutral and arctic cold will thus be available though its impact will not nearly be severe. Unless this changes it could prove to be just what the doctor ordered. We want the jet to relax a little, especially in January, but not too much to allow a thaw. There are indications that precipitation returns to the region as well after what we think is an extended stretch of dry weather.  


No comments: