"Norlun Trough" Gives Part Of Maine A SUPER White Christmas

A Norlun trough, the dotted orange line on this map
from the storm off New England to southern Maine and 
beyond, caused heavy snow in parts of coastal Maine
Image from YouTube, Tim Kelley

 Northern New England is enjoying a white Christmas thanks to a mid-sized storm that passed through the region Tuesday and part of Wednesday.  

A section of Maine is really buried in the snow thanks to an unusual and hard to forecast phenomenon known as a Norlun Trough. 

We're geeking out a little, but here's what happened. 

As WMTW in Portland, Maine tells us, this trough is named after Steve Nogueira and Weir Lunstedt, two meteorologists who coined the term in a 1993 paper describing the phenomenon.  

They were researching a storm that dumped one to two feet of snow in parts of Maine in March, 1992. 

A Norlun trough is an elongated trough of low pressure extending outward on the northwest side of a storm sitting offshore.

The air over the ocean is cold, except for a thin layer near the surface which is heated by the relatively warm water. 

The trough is essentially a weakness in that fortress of cold air keeping that warm ocean air near the water surface. The warm ocean air shoots upward into that weakness/trough. It hits cold air above, and the moisture condenses into snow and blasts down on a small area along the Norlun trough.

More warm ocean air gets sucked into the vacuum created by that initial sharp updraft to keep the snow going. Heavy snow will fall in one spot until the Norlun trough moves away or breaks up. 

Norlun troughs are very hard to forecast, since they drop their heavy snow in a very small area. The National Weather Service office in Gray, Maine did manage to anticipate the Norlun trough Monday evening. Their forecast discussion at that time forecasted two to six inches so snow in most places. 

The forecast discussion also noted, "A Norlun trough setup may bring isolated amounts of up to a lot somewhere on the central Maine coast."

They underestimated it a little, but forecasters almost always do. But kudos to NWS/Gray for catching in advance. That doesn't always happen. 

Wednesday's Maine Norland trough meant business. Brunswick, Maine was buried beneath 16.8 inches of snow. Durham and Litchfield, Maine reported 15.5 inches. Freeport has about 16 inches. But just 20 miles away, around Portland, there was just five or six inches of new snow.  

Norlun troughs can extend inland all the way here into Vermont but their effects are often diminished this far inland.  I notices the trough Wednesday morning extended into the Northeast Kingdom, and snowfall was slightly higher there than in other parts of the state.