Winter Weather Advisory up for Snow/Ice

The National Weather Service in Taunton has issued a Winter Weather Advisory for much of Southern New England.
NWS Boston advisories as of 12/28/15 911 AM
A quick burst of snow will quickly give way to sleet and freezing rain before changing over to plain rain later Tuesday.  The initial burst of snow and the ice will contribute to a difficult AM commute tomorrow.  One silver lining is that many people are off this week so the roads will not be as congested as usual.

General Overview
The storm system responsible for the devastating twisters this weekend and the strong snows is on the move.  At the same time our first real cold high pressure of the season is sending cold air into New England.
WPC surface analysis 7 am Monday with general motion of major weather players
The easterly motion of the high will help lock in the cold air.  At the same time the north northeast motion of the low will help warmer air surge north.  The initial meeting of these air masses should cause snow to break out tonight.  The first precipitation reaches Western New England between 12-1 AM while it gets to Worcester, Hartford, Boston, and Manchester between 2-3 AM.  Surface temperatures at this time project to the upper 20's in Central/Western MA and Northern CT and 30's SE MA, RI, CT.
12z NAM hires 2 m temps 3 AM (image Weatherbell)
Temperatures aloft support snow at this time.  Here are the temperatures at 5000 ft
12z NAM hires 850 mb temps 3 AM (image Weatherbell)
As the low surges towards the Great Lakes and the High dives east the warmth will want to overtake the cold.  However given the density of cold air the warmer air will be forced up and over this layer.  This will transition to snow over to sleet and freezing rain.
WPC surface forecast 7 am Tuesday
I actually think this map is overdoing the snow in Massachusetts.  I expect sleet and ice to be taking over around 6-7 AM.  Surface temps at 7 AM are right at freezing or just below for interior MA.  Notice mid to upper 30's in coastal areas.  It should be flipping to rain in these areas but the roads will still be slippery from the first burst of frozen precip.
12z NAM hires 2 m temps 7 am Tuesday (image Weatherbell)
Temperatures at 5000 ft will be cool, but up at 10000 ft the warm air will be melting the snow layer for Southern New England.  Northern New England should still be snowing tomorrow AM.   By 1 PM the warm air have won out.  A secondary low pressure will form and track just offshore Cape Cod.

12z NAM hires 850 temps 7 am (top) 1 PM (bottom) (image Weatherbell)
In general snow amounts will be light and most will wash away in Southeastern New England.  Here is the National Weather Service most likely snow totals.  Looks like 1-3 inside 495 and south of the pike with 3-6 north and west.  Totals are higher in Northern New England.
NWS Boston most likely snow forecast
Here is New Hampshire, Southern and Western Maine
NWS Portland snowfall forecast
It doesn't take much ice to cause a mess.  Some areas of Western MA and Southern VT are likely to see almost 0.25" which is enough to take down branches and power lines.
WPC Tuesday ice probabilities at least .25"
All in all the storm will be a typical early winter slop storm.  Another shot of rain is likely Wednesday night into Thursday.  Temperatures for the winter classic look to be in the upper 30's on Friday.  If anything major changes I'll update but that's all for now.

-Zack Green


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