By Terry Eliasen, WBZ Executive Weather Producer

BOSTON (CBS) — It has certainly been a winter of unusual snowfall events and this one is no different!

The snowfall we will receive Friday and Saturday will not come from your typical area of low pressure riding up the coast, but instead from a complex interaction between an “Alberta Clipper” to our west and an intensifying ocean storm well offshore.

A bridge of sorts will be created between these two storms, something us weather geeks call a Norlun Trough.

So what the heck is a Norlun Trough? To summarize it is essentially a weak disturbance in the atmosphere which extends much like a tentacle from the parent storm far to the northwest.

This disturbance feeds on winds which converge at the ground level and cold air at upper levels of the atmosphere. Both of these components result in rising air…rising air creates clouds and precipitation, and in many of the Norlun Troughs the air can rise very sharply creating heavy snowfall in very localized areas.

The trick besides recognizing and forecast these events is attempting to decipher exactly where the heavier snow band or bands will set up.

The Maine coast is the most popular spot in New England for heavy snowfall in Norlun Troughs, but we have certainly seen our share of heavy snow in Southern New England as well…the most recent event coming to mind was back in December of 2007. It was a traffic nightmare that many will never forget.

So to summarize for this event…Snow begins Friday afternoon, fairly light in most areas. It looks like two heavier snow bands will form, one in Southern Connecticut extending up into the Berkshires and the other one along Coastal ME/NH and perhaps into Essex County in Massachusetts.

The snow amounts will be a general 1-4” everywhere and some higher amounts in those areas affected by the heavier bands, 4-6”+ possible there.

Snow tapers Saturday evening, and just a few flurries and snow showers thereafter.


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