Snow - Icy Christmas Eve at the lake

[CanisLupusArctos]

A winter weather advisory is in effect for all of New England except the immediate coast through 4 p.m. and may need to be extended. In northern New England 2 to 4 inches of snow will fall and will change over to several hours of light freezing rain. In southern New England, especially south of Boston, the snow will change over by noon and the freezing rain will change to plain rain by mid-afternoon. North of Boston, the ice will last longer.

Currently the National Weather Service is guessing that the change to plain rain will happen in late afternoon over northern New England but based on recent trends with these situations, I am inclined to think it will take longer and the freezing rain may last into the evening. This weather is being caused by a warm front approaching from the south. In the past several weeks I have noticed that warm fronts have not been coming through as quickly as forecast, and have been stalling to our south for up to 24 hours.

Also, weather forecasts rely heavily on 3D computer models of the atmosphere. These computer models, like any other form of automation, often aren't aware of small details like people are. In this case, the models are probably thinking about what's normal for December 24 without considering the small detail that New England's snow coverage is unusually complete (and very deep in some places) for the date. The extensive snowpack is serving as "ice at the bottom of the cooler."

Therefore I would not be surprised at all to see freezing rain linger through the evening hours in areas north of Interstate 90 (the Mass Pike) and west of Interstate 95. The official forecast has the advisory in effect until 4 p.m., but this may need to be extended... and only time will tell.

In the meantime expect a very slick, slow ride today on all of New England's roads. The day will start off snowy but change to freezing rain as the warm air rides up and on top of the cold air that has been with us. Rain from above will fall into the cold layer at the surface and freeze instantly. Remember even though the freezing rain is expected to be light, it doesn't take much freezing rain to render your car's brakes useless. What looks like wet pavement may actually be ice.

One other thing to watch for... especially in VT - NH- ME today and tonight... is the fact that the snowpack might chill the lowest 2 feet of air at the ground even after the official reported temperatures rise. Air temps are usually measured at 4 or 5 feet above ground where people's torsos are, but cold air sinks, and today we may see sub-freezing temps hang on at foot level... causing ice... even after the torso level warms above freezing. You may notice the temperature saying 35 degrees and wonder why the rain is still freezing on contact. It is hard to predict, but be aware that it is possible.