Welcome to the weather blog - a regular Monday through Friday discussion of the weather! While the discussions usually will only come on days I'm working, I'll issue special updates when the weather warrants. I will always post to let you know when no discussion is expected if I'm away on vacation, etc. - if no update is here and no info is available, that likely means the server has temporarily gone on the fritz and I will update as soon as technically possible. You'll find a quick weather synopsis linked to the daily forecast at the top of the page, a general non-technical weather summary below, and when available (most days) a detailed technical meteorological discussion will follow by mid-afternoon. My email is contact@mattnoyes.net. This blog is for you, so I hope you enjoy it! -Matt Noyes
General Weather Summary:
Merry Christmas! The center of a fair weather cell - an area of high pressure - is moving southeast across the Northeastern United States on this Christmas Day, and that's helping to hold cool and dry air in place across New England for the time-being. Nonetheless, the air in place is only marginally cold - that is, borderline for rain or snow across the six-state region - and that will become very important as moisture streams northward from the Gulf of Mexico. By the time all is said and done, this next slug of moisture and the associated strengthening storm moving across New England will deliver a dumping of snow to the Northern Mountains, and mostly rain farther south.
The first signs of increasing moisture have already become evident as high-altitude clouds across an earlier sunny Christmas morning sky. These clouds will gradually thicken throughout the day, and showers will develop across Southern New England around dinnertime. In fact, late-arriving dinner guests may come with umbrellas! You can follow all precipitation through the radar links at right over the course of the evening. For many of us, daytime temperatures in the 40s and 50s will leave an atmosphere too warm in the lower few thousand feet to support any snowflakes, and raindrops will be the result. The air, however, is dry, and where saturated the temperature will fall so that some higher terrain will cool sufficiently for rain to change to snow. This phenomenon should take place from the Berkshires to the Worcester Hills between 10 PM and midnight before changing back to rain as warm air is swept in on a southerly wind, while areas farther north will see a longer-lived period of snow. For many areas of Central and Southern New Hampshire, Vermont and Maine, any snow that falls will be rather wet and sloppy, leaving some slush in communities like Concord, NH, and perhaps Portland, ME, for the Tuesday morning commute, where snow should have changed to rain by that point but melting of the coating to an inch that will have fallen will still be underway. Farther north still, our marginal airmass should be just barely on the cold side of that margin, meaning that most of what falls in the Northern Mountains will be snow.
In the North Country, equally important to determining snowflakes are likely to fall is the ratio of snow to water - that is, I'm expecting some of Northern New England to receive .75" of liquid equivalent precipitation Monday night through Tuesday night, but the temperature of the atmosphere aloft is what's critical in determining the type of snowflake that will fall. With temperatures just barely below freezing in the lower several thousand feet of the atmosphere, conditions will be favorable for large aggregates - that is, huge flakes that are wet in nature and will compact quickly, limiting how quickly they can accumulate. The higher one is in elevation, the less sky snowflakes will have to travel through at near-freezing temperatures, and therefore the lighter and fluffier the snow will be. This should result in a large difference in accumulation between valley and mountaintop, with higher amounts in higher elevations.
In Southern New England, Tuesday morning showers will linger through the day - but truly only as showers and drizzle and unlikely to be a steadier rain thanks to very dry air moving overhead several thousand feet in elevation. This dry air will make most of the clouds over Southern and Central New England too shallow to produce widespread significant precipitation. Farther north, more moisture will be available deeper in the atmosphere, and a new swath of upper level energy will swing through during the afternoon - two good reasons to expect periods of steadier and heavier precipitation to continue.
By Tuesday night, colder winds will blow from the northwest, and this will result in "upslope flow", where air flows up the Western slopes of the Green and White Mountains, forcing the air upward, resulting in clouds and precipitation, which is why I'd expect snow to linger along these mountain slopes through Tuesday night, with some additional accumulation. Elsewhere, a few flurries are possible with the onslaught of colder air, though for the most part a drying trend will begin Tuesday night and continue into Wednesday and Thursday - two chilly and breezy days with a blend of sun and clouds ahead of the center of another cool Canadian high pressure center.
By late in the week, this cool fair weather cell will merge with another, larger bubble of high pressure moving over the Mid-Atlantic coastline, and this will mean a moderation in temperatures for Friday. By next weekend, another energetic upper level disturbance will be ejecting east after churning across the Rockies and Plains, resulting in another swath of moisture pluming out of the Gulf of Mexico and thereby bringing another likelihood of rain - perhaps mountain snow if cool air can hold on long enough.
Technical Discussion: None today...have a wonderful Christmas!
Matt
