As you know, I was never too impressed by this storm and the trend over the past 24 hours has been for the computer models to push the track farther east/southeast making this less and less of a big event for Maine. The southern half of the state will still see some plowable snow, but this won't be a high impact storm for most of us.
Today: Some decent "pre-storm" bands have already formed across western and central Maine this morning. This exact setup has been in place with most of our winter storms this season: As the inland low transfers its energy to the coastal low to our southeast there is a moisture convergence directly above Maine leading to snow breaking out well ahead of the actual storm. (This is a Miller Type B storm. Here is my explanation of that term from this week's Ask Keith segment) These bands of snow will be generally light and intermittent but I can't rule out of a few moderate bursts especially across western Maine with some terrain enhancement there. (One thing we have working in our favor here is that the "boundary layer" temperatures are pretty warm, so that makes it harder for the snow to stick to the ground). When it's not snowing look for mostly cloudy skies and temperatures in the mid to even upper 30s. Northern Maine may even see a few glimpses of sun and conditions there will remain totally dry.
Tonight: By this evening the energy transfer will be largely complete and there will be a coastal low pressure system basically due south of Cape Cod, MA. This low position, as I harped on all week, is just too far south and east to create a large storm for us. Instead look for mainly light snow to push slowly from south to north through the evening, arriving in York county around 8-9 PM and then pushing to the Midcoast by 2-3 AM and finally to Bangor by 5-7 AM Sunday morning. This part of the storm looks the most widespread as far as snowfall coverage but the dynamics look WEAK in the upper atmosphere so I foresee mainly light snow all the way until sunrise on Sunday. North of Bangor and east into Downeast it's basically dry through the evening with mostly cloudy skies.
Sunday: The coastal low will being pulling away almost due east at this point and the main focus of the snow will become an inverted trough that connects the coastal low and the dying inland low which will be located in Canada at that point. This is, in essence, a NORLUN trough. You know ALL about how hard those are to forecast so it's all about where, exactly, this trough sets up in relation to the Maine coastline. To me it looks like it will setup from Portland to Belfast and that will be the region of enhanced snowfall through Sunday midday and into the afternoon. Away from this area of enhanced snow look for just light snow with breaks of dry weather and cloudy conditions. In short, it will be snowing from time to time, but for most of us it won't be a big deal. I've made an accumulation map that speaks to this and tries to pinpoint the area of the inverted trough the best way possible. The snow that falls will be of the heavy, wet variety as surface temperatures hover at and above freezing.
By Sunday night most of us will be done with the snow but coastal locations in the path of the inverted trough will continue to see at least light snow. (Again this is likely from Portland through the Midcoast). After midnight everyone clears out and goes to a mixture of partly cloudy skies.
After morning clouds on Monday look for rapidly improving conditions by noon with a mostly sunny afternoon on tap. Temperatures will be reasonable enough, in the upper 30s to low 40s.
Tuesday starts with sun but ends with clouds as our next storm system approaches. This one will arrive Tuesday night and after a brief mix the coastline will go to all rain by Wednesday morning. The mountains may hang on to snow for long enough to accumulate but I'll get a better handle on this for you once today's little storm is out of my hair.
After Wednesday we set into a classic blocking pattern with one of the biggest upper level lows I've ever seen spinning directly overhead. As I said yesterday, an upper level low of this size means one of two things: Either we are going to get one mega blizzard or 3-5 days of off and on snow and snow showers. I still don't know which one of the two options we will get...no one does. But I'm going to keep a close eye on it for you.