As the graphic above depicts, snow is will be moving into the area early tomorrow morning in southwestern CT and move northeastward to encompass much of southern and central New England. However, with current forecasts from the NWS, this brief period of moderate snow will likely change to sleet and then plain rain south and east of Interstate 95, including Boston, Providence, Plymouth, the Cape, and much of the South Coast.
Why is this going to occur?
Well, currently the ocean water right off the coast is all the way up into the lower 40's. A buoy in Boston Harbor currently reads 41 degrees. This is unusually warm for this time of year. Usually sea surface temperatures should be in the 35-40 degree range at this time of year at the end of January. With the easterly winds we will endure much of the storm, all of this warm air from the Atlantic will overspread the lower and mid levels of the atmosphere, changing any snow over to rain, heavy at times. Further inland, away from the influence of the ocean, anywhere west of I95 or Rt. 128, there will be colder air with temperatures around 33 or 34. This will be a marginal temperature for snow or rain. It could easily go either way. However, along the coast temperatures should rise safely above freezing to around 37 or even 39 degrees. Outside of Rt. 495, there will be some of the coldest air where temperatures will likely stay around 30-32 throughout the storm, making most of this event, a snow event.
Now that you know the temperature story of the storm, how much snow and/or rain is going to fall?
Well, down on the Cape and South Coast, expect possibly a few wet flakes early on, but that will rapidly turn to ALL RAIN and you may pick up one half to three quarters of an inch of rain.
From Plymouth N&W to Providence and Boston and just N&W of Boston by 5-10 miles, expect a brief period of light to moderate snow which will likely accumulate to around an inch, maybe two, but much of it should be washed away as it too will likely change to ALL RAIN by the noon hour and become a light to moderate rain as well.
From NW of 128 to 495 including NW RI, here is the tricky part of the forecast as one degree could make all the difference between mostly snow or snow to rain. This area includes cities such as Lowell, Lawrence, Burlington, Concord, Natick, Framingham, and Acton. Here accumulations should be on the order of one inch if we quickly change to rain, but if we stay more of a snow event as some forecast models are now indicating, we may pull out with 3 or 4 inches of snowfall. This will be VERY close.
N&W of 495 including the cities of Worcester, Fitchburg, Charlton, and Princeton this is where it should be mostly a snow event with high end Advisory type snows likely. A few spots may even see low Warning type snow, 6" or 7", in the highest of elevations. Generally we are talking about 3-6" of snow.
Currently in the Berkshires of MA and the Litchfield Hills of NW CT, there is a Winter Storm Watch. Here they may have temperatures stay in the upper 20's to around 30 throughout the storm and may see the most moisture as the will have upslope winds off of the Berkshire Mountains. This will make the eastern slopes of the Berkshire Mountains pick up the most snow in the snow event. I am currently thinking snow accumulations will be on the order of 7-10".
Again, this looks to be a western New England snow event and eastern New England will just have to wait their turn. It will happen again this winter. I think...
I will post a snowfall accumulation map later in the day as the details of this storm become more certain. Stay tuned, especially if you live in Worcester County and beyond...