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Monday, December 22, 2014

Through the holidays and beyond

Through most of this December, Northern New England has been one of the few places east of the Mississippi to actually enjoy some assemblance of winter. This remains true as of early in the Christmas week. Temperatures have begun their rise over a large expanse of the country but readings remain below freezing under clouds across much of the Vermont high country. This is about the only good thing I can say in the short term. It is not very advantageous to be anywhere in the east during the Christmas holiday, Vermont included.

Moisture from a piece of the approaching storm system will arrive Monday night as some snow, accumulate a few inches then turn freezing drizzle or some freezing rain during the midday hours Tuesday. Some locations are indicated to get above freezing during the day Tuesday but I think much of the mountain can hang on to 32 F for most of the day. Models do indicate a more organized area of rain, arriving Tuesday night which will likely fall as some rain in most places and freezing rain in some.

A massive surge of mid-layer tropospheric warmth is expected to arrive by Wednesday morning. Most of this air will remain a couple thousand feet above the surface and it could provide one of those rare situations where the summit of Mt Washington out does all the valley locations on temperature. Even the summit of General Stark could warm to near 40 by late Christmas eve before valley locations do the same by early Christmas morning. There is no avoiding the rain however. It will remain sporadic through early Christmas eve then turn heavier during the day. I am hoping the temperature inversion will keep the winds down since high winds combined with high dewpoints and rain can eat away at snow very quickly. Models do indicate a small window of time early Christmas day when some of the excessive mid-level warmth could mix down to the surface allowing temperatures to surge (perhaps as high as 50). This would occur just as some of the better frontogenetics are pushing through the region allowing for the possibility of very heavy rain and even a thunderstorm. The pain should be over with by later in the day on Christmas and temperatures will fall back toward the freezing mark by the 26th.

The overall weather pattern is expected oscillate quite violently over the next several weeks. A loosening of the jet in the Pacific combined with the development of the large upper level ridge over Alaska and the Yukon will support a turn toward colder temperatures. The arrival of the cold in Vermont will have to wait until the 28th (both Friday and Saturday following Xmas could see readings sneak above freezing still). The combined presence of Arctic air in the days before New Years along with a trough position in the middle of the continent does provide an inviting open door for a substantial winter weather event around or just before New Years Day. Medium range models have gone back and forth on this; but in this update, it is a small island of hope in a sea of bad news.

The Madden-Julian Oscillation or MJO is what has many in the meteorological community talking over the last few days. At least as it pertains to weather as we head into January. I don't want to get too bogged down talking about the phenomena, but to put it as simply as I can, the MJO describes a cycle of convective thunderstorm activity near the Indian Ocean. There are several phases of the MJO and each phase can have an impact on the Jet Stream in the Pacific, how loose or tight it is and whether or not we will see an evil empire. The MJO has been very disappointing this month. It spent a number of days in adverse phases for us and has since proceeded toward neutrality without fully rotating toward favorable phases. By early January, it is now expected to move back into treacherous ground for us. This is a big reason why some of the ensemble guidance has allowed the cold pattern to flop just after the New Year. We don't have total agreement on some of this but there are enough indications to suggest that the cold will retreat again in early January. If it's a modest retreat, we can still hold out hope for some snowfall but a full retreat could put a hurting on us again. We shall see.

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