HEAVY SNOW ANTICIPATED NEW YEAR'S DAY AND EVENING...DEEP COLD LATER THIS WEEK TO BE FOLLOWED BY STRONG WARMTH

MONDAY MORNING UPDATE:  Happy New Year!  A more extensive update to follow as soon as I can get it out, but while there will have to be some changes to the forecast I posted yesterday regarding accumulation amounts, this is still a dynamic and potent storm that will try to throw a few surprises our way.  Perhaps the most important factor here is the very favorable Atlantic Ocean inflow of moisture that sets up late this afternoon and evening that will result in a sudden and marked increase in snowfall amounts...probably somewhere in Northeastern Massachusetts.  The end result will be for me to cut WAY back on accumulations along and near the Massachusetts Turnpike into Boston, with the axis of heaviest snow now expected farther northeast than I thought 24 hours ago - focused from SE New Hampshire up the Maine coastal plain.  I'll get more out soon!

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The break between weather systems is perfectly timed for our New Year's Eve, with mostly dry weather expected for many communities, excepting mountainous locales where snow showers and squalls will continue into the first part of the night.  Elsewhere, the weather will cooperate for First Night festivities before a pounding snow returns to many spots on New Year's Day, followed by a bitter blast of cold, then eventually surging warmth by next week through next weekend.

For now, the departing area of low pressure that moved south of New England did its dirty work in the form of over a foot of snow in Central New Hampshire, and in parts of Eastern Maine.  Six to ten inch amounts were common in Central New England, otherwise, though there was a sharp dropoff in far Southern New Hampshire and parts of Northern Massachusetts points southward, where the combination of a mix with rain and a dry slot both held accumulations in check.  With that storm exiting stage right, cool air remains in place across New England, though deep cold is still locked in Canada, meaning some melting is taking place regionwide on our roads and walkways, and a refreeze will slowly occur overnight Monday night.  Though that will mean patches of black ice, conditions couldn't be much better for First Night festivities - warm enough for revelers to enjoy, and cold enough to keep ice sculptures looking wonderfully.  Skies will gradually clear away from the mountainous terrain where a few snow showers will continue, and winds will gradually subside between 5 PM and midnight.  This will be a good combination for cooling in deeper valleys of especially Northern and Central New England, where temperatures will cool into the teens, while they hold in the 20s farther south.

Marching across the Midwest as of this writing is our next disturbance - innocent looking and rather small in coverage, but a nasty and intense upper level system that's packed with energy and ready to unleash it.  As this system approaches the Northeast, it will strengthen considerably, developing a closed counter-clockwise circulation and eventually tapping Atlantic moisture.  The combination of energy and moisture will result in a round of very heavy precipitation later Tuesday.  In advance of the system, some sun will probably shine early New Year's Day, then fade behind quickly advancing and thickening clouds.  By midday, snow will be developing in most of Western New England, moving east out of New York State and not yet at maximum intensity.  At the same time, in response to the strong upper level disturbance, a surface low pressure center will develop near the Connecticut South Coast and will move east across extreme Southern New England, where it will cross Provincetown, Massachusetts while strengthening Tuesday evening.  There are a few results from this process.  The first is to cause intensifying precipitation simply by virtue of the strong upper level disturbance, and the difference between the cold air it brings aloft, and the relatively warm air near ground level.  This difference in temperature with height is referred to as instability, and is the same parameter we speak of with regard to thunderstorm growth - evidence that the atmosphere will be primed for deep and healthy cloud development.  The next factor is the developing "cyclonic," or storm, circulation that will be rotating counter-clockwise.  This will pull ocean moisture in, especially when considering that the strong upper level disturbance will really result in a total of three surface storm centers - one in New York, one moving over far Southern New England, and another over the ocean.  Together, the three of these will develop a conveyor belt of moisture off the Atlantic and into New England.  Finally, there will be a rather stark contrast of air over New England - relatively warm and moist air to the south and southeast of the storm, and colder, drier air to the north.  As the storm strengthens, this dividing line of air is going to align at all levels of the atmosphere later Tuesday, creating a sharp rain/snow line.  In the process leading to that convergence of airmasses, though, there is some ambiguity, and this lack of clarity will be the reason for uncertainty leading right up to the storm Tuesday afternoon.  At issue here is how long the relatively warm surface air - in the middle and upper 30s - can hold on in especially Southeast New Hampshire and Eastern Massachusetts.  Though computer guidance suggests that warmth, helped by a southeast flow during Tuesday afternoon, will hold on enough for rain before a change to snow, I have trouble believing that scenario.  While rain would seem likely in many of these Eastern areas to start, a strengthening storm serves as a vacuum, pulling air toward its center, and a northeast or even north wind seems likely to develop Tuesday afternoon, tugging cold air toward the storm center and allowing for a quick flip to big, fat snowflakes that will become heavy quickly.  These northeast winds will hold marginally cold enough air in place, especially from the Massachusetts Turnpike northward, for a blast of heavy snow.  As the moist Atlantic inflow strengthens, snow will easily reach all the way to the Canadian border, and most of Central and Southern New England will find a period of heavy middle afternoon, late afternoon, and evening snow, developing from west to east between midday and 2 PM, respectively.  Farther south and closer to the coastline, around the immediate Boston area, rain will hold on longer, but still should snap to snow as the storm strengthens over Provincetown Harbor, and should provide a couple hours of intense snow as moisture wraps around the storm center.  This wraparound snow would be less intense the farther south one is, but in the hardest hit areas - those who see mostly snow in Central and Southern Vermont/New Hampshire, Southern Maine and Northern Massachusetts, Tuesday late afternoon and evening snowfall rates may reach two to three inches per hour!  This would drop nearly a foot of snow in only 6 hours, and would create a travel mess through the first half of Tuesday night as road crews would fight to get caught up for much of the night, even though the heaviest snow would be done by 8 PM. 

Overnight Tuesday night, mostly cloudy skies would prevail, and snow squalls would be likely in Northern New England after midnight, perhaps carrying into Central New England in the predawn hours with the passage of an arctic cold front.  This finally taps deep arctic air from Canada, sending it southward with temperatures quickly plummeting to the single digits north, teens central and 20s south by Wednesday morning, and slick spots where the squalls moved through.  Wednesday will follow suit with an active northwest wind and a cold day of highs only in the 20s for most spots and teens north, with plenty of clouds mixed with Central and Southern New England breaks of sun.  Winds will gust to 40 mph at times, creating wind chill values in the single digits for many spots.

Believe it or not, colder air will follow!  A reinforcing cold front Wednesday night will drive another shot of Canadian chill southward, driving low temperatures to either side of zero in many spots by Thursday morning, and holding daytime high temperatures in the teens to near 20 for most of us, single digits in Northern New England with an active wind that will keep wind chills below zero through much of the day.  This cold will moderate somewhat by Friday with a few high clouds the indication of warmer air making a comeback, and a steady warming trend will follow for the weekend.

Of course, one extreme begets the next - doesn't that make sense in a season like this?  Warmth over the Equatorial Pacific will move into the Western United States and Southern Canada next week, trudging east and moving into New England as the week wears on.  Not only are a few if not several days in the 50s likely, but if the forecast verifies based upon the predicted weather pattern, 60s would even be a possibility by next weekend for some of New England!  Winter lovers shouldn't fear, though, signs are that while the warmup may last several days, cold air returns by the end of the month.

That's all for today.  A very happy, healthy and Blessed New Year to one and all.  I'll be off tomorrow, but will issue a quick update if needed for the storm.

Matt

Comments

[David Majercik]

Re: "Something to note:" Unlike rain, snow depth depends largely on temperature. Also, those measuring (like me) probably also include any accumulated sleet, graupel, and frozen rain. Thus, unless water content is measured, record or non-record snowfalls are inherently suspect. But if water content is measured, what fun would it be?

[Tony McGee]

Something to note:

December 2007 the snowiest on record for Concord, NH... The snowfall today brings the December, 2007 monthly total to 44.5 inches. This breaks the previous record December snowfall of 43.0 inches set in 1876.