Metro Boston, North Shore and Metro West: Wednesday will be the last pleasant day this week as we get into an active pattern kicking off with a significant winter storm Thursday. Expect a lot of sunshine today with light winds. Temperatures will continue to run some 10 degrees below normal.
The National Weather Service has issued a Winter Storm Warning for most of Middlesex County from 7 am Thursday until 7 am Friday and a Winter Storm Watch for western Essex County for the same time period. Eastern Essex, southeast Middlesex and Suffolk Counties are not under any warning or watches at this time. That can change.
All eyes look to the south where a storm system is dumping ice and snow across portions of the south and mid-Atlantic region. Low pressure will move off the Southeast US Coast Thursday and intensify as it moves northeastward. By Thursday evening the storm is expected to be centered near the Virginia Capes, tracking over southeast Massachusetts and into the Gulf of Maine Friday morning. This track is further west and brings the storm center near the Cape Cod Canal late Thursday night. With this scenario we should expect snow everywhere Thursday morning, mixing with and quickly changing to rain along the coastal plain in the afternoon with the rain snow line continuing to advance inland into Thursday night.
Breaking down the scenarios by area: Along the coast and inside of Route 95 the snow may accumulate 2 to 4 inches, highest amounts away from the immediate coast, before the change to rain in the afternoon. Along Route 128, west and northwest of Boston, snow hangs in a few hours longer before mixing with rain in the afternoon. There could be a period where the precipitation flips over to all rain late in the day. Snow accumulations of 4 to 6 inches before the mixing and or changeover occurs. Along Route 495 it should remain mostly snow all day with some mixing of rain and sleet late day. Accumulations of 6 to 10 inches, perhaps close to a foot across parts of northwest Middlesex County.
The rain snow line is expected to advance to at least the Route 128 corridor and perhaps a bit further west than that, somewhere between Route 128 to Route 495. The longer it takes to mix and change to rain the more accumulating snow you will get.
A word of caution. This forecast is still a work in progress and will probably be so through the day and night because if the storm track shifts further inland then so does the rainfall and those accumulation amounts just mentioned will be lower. If it tracks further south, say between Cape Cod and Nantucket Island the snow line collapses closer to the coast and accumulations increase, especially away from the coast. Please keep that in mind as this is still a very tricky forecast for northeast Massachusetts and the metro Boston area.
As the low pulls away Thursday night it should get just cold enough so that everyone changes back to snow before the precipitation ends early on Friday. An additional light accumulation of snow is possible.
Conditions improve during Friday before another weak disturbance approaches with a chance of light snow or snow showers late Friday night and Saturday. Then, another cold shot Sunday.
Expect increasing winds during Thursday and continuing overnight. Highest gusts along the coast.
Because of low astronomical high tides coastal flooding is not expected to be significant. However, beach erosion and some minor flooding is possible during Thursday nights high tide cycle.
72 Hour Outlook:
Wednesday and Wednesday night: Sunshine and cold today, increasing clouds late. High temperatures approaching 25 degrees. Quickly turning cloudy tonight. Chance of snow by daybreak. Not so cold, lows in the upper teens inland to low 20s coast. Light winds.
Thursday: Snow, may become heavy at times through the morning, mixing with and changing to rain along the coast in the afternoon. Snow mixes with rain interior by later in the day, possibly changing to rain for a time. Mainly snow well inland along and west of Route 495 with a chance of some rain and sleet mixing in for a time. Highs from the upper 30s coast to low 30s interior. Increasing east to northeast winds with gusts of 35 to 45 mph possible along the coastal plain.
Thursday night: Precipitation changing back to snow before winding down and ending. Lows in the upper 20s to low 30s. Continued windy as winds back to north and northwest with gusts to 45 mph possible along the coast.
Friday: Chance of early snow showers. Partial clearing by afternoon. Blustery, highs in the 30s and winds gusting close to 30 mph.
Friday night: Chance of light snow or snow showers. Lows in the 20s.