1030pm

Good evening everyone! Sorry this is being posted later than I wanted. But a busy day will do that…

We have yet another bout of winter weather on the doorstep, moving in from the southwest for Tuesday. This storm, though not nearly as powerful and heavy precipitation-wise as the last, is slated to bring more of a variety of precipitation over a larger area. Whereas the last storm’s rainfall was confined mainly to the immediate coast and Cape Cod, this one will send a sleet/freezing rain/rain swath over a fairly large area of eastern MA and coastal NH.

Instead of getting into technical aspects of the storm, all that really needs to be said is that this particular setup will allow warmer air in above us, resulting in the mix and change in many areas, after starting as snow. The surface remains very cold thanks to a cold airmass in place and a deep snowcover from the recent storm. This results in a rather messy setup.

What to expect, and when…

This storm should start as snow everywhere in eastern MA and southern NH. The snow area is expected to advance north across the region during the morning, starting around 6am south of Boston and by 8am to the north, lastly in southern NH, and of course + or – about an hour either side of these times. The amount of snow that falls will depend on how quickly an area of moderate precipitation moves up into the cold air in place, while it is still cold enough above us to support snow. My best guess for snow before any mix/change occurs is around 1 inch to  locally 2 inches along the immediate coast, including the city of Boston, 2 to 4 inches just inland from here including the 128 belt, 3 to 6 inches from just outside 128 into the 495 belt, and 4 to 8 inches northwest of here in northwestern Middlesex County, southern NH away from the coast, and Worcester County.  There is an outside chance of an isolated heavier snow amount somewhere in the hills of Worcester County to nearby southwestern NH. Some selected cities and towns and what I expect their snowfall to be, plus or minus 1 inch either side (and if you live in one of these places let me know what you get please!)…

Boston MA: 2″

Woburn MA: 4″

Waltham MA: 3″

Londonderry NH: 6″

Nashua NH: 6″

Chelmsford MA: 6″

Worcester MA: 5″

Fitchburg MA: 7″

Milford MA: 3″

Hampton NH: 3″

If you want a number for your city or town, comment here and I’ll give you my best guess.

The snow will be the least of the problems from this storm for some people. Rain will become an issue for some, due to potential localized flooding in poor drainage areas if it should be heavy enough, and also the issue of snow/rain weight on flat roofs. Icing will be the other story, and trying to pinpoint the area of most significant icing (that is up to 1/2 inch or slightly more of ice buildup from freezing rain) will prove very difficult.

As the warmer air comes in aloft and starts to put an end to the snow from south to north, it will flip to sleet for a time (frozen raindrops, or ice pellets), which generally do not cause major problems) then plain rain closer to the coast and south of Boston where the surface temperature is above freezing, but freezing rain (or rain that comes down and freezes to a glaze of ice upon contact with the ground, or the snowcover). The glazing takes place in areas where the surface temperature is at or below freezing. I’m still not sure where this changeover line is going to make it to. A best guess at the moment is that it will make it into coastal NH and most areas along and southeast of Route 95 in MA fairly easily. The areas near 95 will probably see a period of sleet & freezing rain with some minimal glazing before it goes to plain rain during the afternoon Tuesday. As you go further west and north, the changeover will occur later and the sleet to freezing rain will occur longer. As I see it, the most likely areas to see icing of 1/4 to 1/2 inch or slightly more will run from the MA/NH border through Lowell/Chelmsford, southwestward through the central part of Middlesex County including the Concord area and further southwest from here down toward Worcester. This significant icing belt may be only about 10 miles wide, so we’ll have to watch radar and surface observations to see where it sets up. North and west of this area, precipitation will remain mostly snow & sleet, but may turn to freezing rain for a brief time.

The main precipitation area should begin to taper off and exit from southwest to northeast during Tuesday night, and be all but over by midnight. Temperatures over areas that get ice & snow will remain fairly chilly and untreated surfaces will be slippery throughout the night. Further south and east, areas that get less ice and more rain may develop some slick spots as temperatures fall to near or slightly below freezing, especially if there are any breaks in the clouds, which would allow it to cool more quickly.

Caution should be used in all areas for any travel Wednesday morning.