Ten things to know about the first spring storm _ wcsh6.com

2) Surprise, surprise, late season snow events are not that uncommon in Maine. Dating back to 1882, when weather records began in the Greater Portland area, there have been 73 snowstorms of 6″ or greater in the month of March. There have been 20 snowstorms of 6″ or greater in the month of April. There has been 1 snowstorm of 6″ or greater in the month of May. That’s a total of 94 snowstorms of 6″ or greater over a 134 year span. Do the math, out of a span of 10 years, 7 of them will feature a 6″ or greater snowstorm…they’re actually very common!

4) The synoptic set-up does not support a widespread New England snowstorm. At focus here is the northern jet energy and how quickly it links up with the southern energy. Timing is critical and this delicate phasing process will ultimately determine how much and where substantial snow will fall. It is safe to say that the coast will see the most snow, but does that include the entire Maine coast, the Mid and Downeast Coasts or just the Downeast coast? Answering this question has proven to be very challenging. When it comes to pinpointing the location of heavier snow and banding, I like to look at the 850mb and 700mb levels of the atmosphere. I’m searching for signs of significant overrunning and or a maturing cut-off center in the low to mid levels. In fact, to the NW of the cut-off is where significant moisture and thus snow formation is occurs. The stronger these levels look, the more substantial the snow will be. Computer guidance has had an incredibly difficult time deciphering the strength and timing of the northern and southern phase with this system over the last several days but there finally seems to be some consensus. The best overrunning for this event will be over Downeast areas. The 850mb low consolidates and cuts-off over Yarmouth, Nova Scotia. That would put Downeast areas 50-100 miles to the NW of the intensifying 850mb cut-off…a prime zone for heavier snow and banding. This is why Downeast Maine is under a Winter Storm Warning. While overrunning is present for the rest of the Maine coastline, it is not as impressive and getting warning criteria snow (6″ or more) will be very tough and is not likely at this time.

5) This is one of the driest air masses we’ve seen all Winter. Current dew points are in the single digits. The dew point is the temperature at which the air would need to be for dew and moisture to form. Clearly we aren’t going to get our temps down into the single digits, so somehow we need to bring those dew points up. That will happen tonight when snow starts falling from the clouds, it will sublimate (the transition of a substance directly from the solid to the gas phase without passing through the liquid phase). Sublimation will both cool the air and moisten it up so the temperature and dew point will get closer and closer until snow reaches the ground. Because there is a large range to overcome, the timing of snow will hold off until after midnight. In fact, it won’t fall for most until 3-4 in the morning. The storm will pull away quickly and end in Southern Maine around noon and late afternoon and early evening in Eastern Maine.

6) The drop off from a lot of snow to none at all will be very impressive. 6″ of snow looks likely in Hancock and Washington Counties…with a chance to see double digit amounts in Eastern Washington county. 3-6″ for Penobscot Bay to around Bangor and into Southern Aroostook county. Southern Maine will see a few inches…likely 1-4″ with highest amounts along the coast. But, if more intense banding, which will be lined up just offshore, sneaks west just a smidgen, we may need to pop up into the 3-6″ zone. That’s about it for accumulation…I can see the foothills getting zilch, and it wouldn’t shock me if the beaches of York county get 3″, yet the Ossipee River Valley, over interior York county gets nothing at all!

10) Blocking over Greenland known as the North Atlantic Oscillation (NAO) has been nonexistent this Winter season. This, along with El Nino, are why it has been so warm the past few months. Well, the outlook going into early April and the start of Spring is for the NAO to go neutral or slightly negative meaning there will be more blocking over Greenland which will force colder than average temperatures south into New England more frequently. This doesn’t mean we won’t have mild days, we will. But, it also means we will have chilly ones too and we probably aren’t done talking about wintry precipitation either.