Saturday February 23, 2013 | 05:45 PM
Posted by David Epstein

Forecasters are certainly going to be earning their money this month.  Here we go again with another very complicated situation unfolding for southern Maine and the seacoast area of New Hampshire.  As you are no doubt aware there is some snow in the forecast for late tonight and Sunday.  The atmosphere is a funny thing, we can try like mad (and it can be maddening) to predict it, but sometimes things unfold very differently than expected.

A few days ago it looked like the storm that gave parts of Kansas so much snow would move to the west of New England and then a new storm would form off the coast and end up giving areas from just west of Boston to Augusta a significant snowstorm.   That would have been a relatively straightforward forecast.  That isn't the case anymore.
While the new storm will still form, it appears that it will be too far east to give us a blockbuster storm. Sorta.  I assume the reason you are reading this is not for a maybe or a sorta, so let me clarify.  There is some indication that a bit of storminess will extend westward from the low pressure area into southern Maine.   You might remember several weeks ago forecasters were talking about a potential big storm from something called a Norlun trough. Guess what, something resembling that situation is back. 
While this is not a true Norlun trough, as those situations have much colder air, it's similar. The Norlun trough is a unique area of low pressure that is actually not very uncommon. Most of you have seen the L for low pressure on the weather maps. That L represents the place on the map where the air is rising and often creating snow or rain. If the low is close enough to our area then we get inclement weather. Often our bigger storms are the result of big low pressure centers. What is unique about a Norlun trough is that the low is very far out in the ocean and would normally be too far away to give New England any precipitation. However, in the Norlun situation a bit of the energy from the low reaches back to the west and connects with another weaker storm often over Ohio or New York. I drew a line on this map to illustrate the connection between these two storms. 
Eventually, the whole system will pull east into the Gulf of Maine which will rapidly move east and end our snowfall. The tricky part of the whole situation is that the exact configuration of the trough is critical to who gets flurries or even rain showers and who gets heavy snow.  Areas close to the trough can see heavy snowfall much like during a lake effect event. Snow can accumulate many inches in a just a few hours. There isn’t much wind with these situations.  In this case it's not going to be very cold and the snow will be heavier and wetter. 
Overnight there will be a period of snow and even some rain this evening, then I expect a break in the action for much of the night.  Tomorrow, more snow will break out during the morning and accumulate much of the day.  Since temperatures will be around 32F, the roads won't end up with as much snow as what falls on the existing snow. (make sense?)  The numbers I have outlined on the map assume that the precipitation moves into southern Maine and doesn't remain off the coast.  These situations are very fluid.  Portland and surrounding areas could see much less or slightly more snow than my map indicates, but for now I am comfortable with a 3-6 inch, call it moderate storm for much of Cumberland and York counties.
If you are curious about the name of this system , the “Nor” comes from Steve NOguieRa, and the “lun” comes from Weir LUNdstedt. In 1993 these two meteorologists authored a paper which described the aforementioned situation that has come to be known as the Norln Trough.


Gardening this week With another storm on the horizon for the weekend you might feel like spring is still very far away. The reality is that in just a few weeks, many of you will be able to get into your gardens and start growing for another year. Earlier this month I went to New England Grows which is a trade show for those who work in the industry. Although not open to the general public, in this week's video I share some of the latest trends and newest plants for 2013. I'll be updating the forecast all day on Twitter at @growingwisdom please send me your reports there.

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About the Author

David Epstein has been a meteorologist for more than 25 years. He spent 16 years in Boston and currently freelances at WGME13 in Portland.

In 2006, David founded, a business producing educational and marketing videos for the green industry. He currently is a professor at Framingham State College, teaches Jan Plan at Colby College and owns Bloomscapes Inc., a landscape design business.

David authored "Gardens Of New England" and his work has been published in Grolier's Science Annual for 10 years. He lives in South Natick, Mass., and has a summer home in Harpswell.

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