Summary: The forecast for the mid-week coastal storm is coming more into focus and I now have a higher level of confidence in the forecast as the storm approaches. However, the scenario remains complex and somewhat “fluid” so additional updates will likely be necessary over the next few days.
Fortunately, I think we will avoid the very large heavy, wet snow accumulations that portions of the Mid-Atlantic will see over the next few days. There will likely be portions of the Appalachians, in northern Virginia, eastern West Virginia, and western Maryland that see between one and two feet of heavy wet snow as the surface low redevelops off the Mid-Atlantic coast and intensifies during the day on Wednesday. Even Washington, D.C. and Baltimore could see 10 inches of heavy wet snow after an initial period of rain. As the storm intensifies, winds will also increase to over 20 mph, which, combined with the heavy, wet snow is likely to cause widespread power outages in these regions.
Even though this scenario is unlikely for Berkshire County, I do think we will see some accumulating wet snow. It looks like the surface low will initially move due east off the Mid-Atlantic Coast during the day and overnight Wednesday, prevented from moving north by the blocking ridge over eastern Canada. The wave containing the “sharp” trough in the jet stream, which was responsible for generating the surface low, will be forced to “break” (wave-breaking) as it runs into the strong upper-level ridge backed up over eastern Canada. As a result, the entire system will be forced to slam on the breaks as the surface low becomes “stacked up” under the upper-level low/trough/cold pool. This is what is called a “cut-off” low. The impact that this will have in the real world (not crazy “atmospheric science” world) is that the system will stall off the coast and cause a protracted weather event for Berkshire County that will begin Wednesday and not end until Friday.
The timeline looks something like this: As the surface low intensifies on Wednesday as it moves slowly east, the strong northeasterly flow around the low (counterclockwise flow-“Nor’easter”) will likely bring low level moisture off the ocean which will be lifted by our local terrain. Therefore, it looks like there is a good chance for snow showers during the day Wednesday, particularly over the elevated eastern terrain, even though the main area of precipitation will still be well to our south. Temperatures will be in the 30s and with a high sun-angle this time of year there should be little, if any accumulation for most of the county. The one exception would be over the elevated terrain to the east where up to 1″ could fall.
As the surface low drifts by to our south Wednesday night into Thursday morning we should fall under the northern edge of its precipitation shield. Light snow will be likely in southern and eastern parts of the county where 1-3″ could fall in the elevated terrain in the southeast (e.g. Otis and Becket). The likelihood of accumulating snow decreases as one moves north and west within the county. Pittsfield may receive and inch or so, and there is only a chance of snow in the northwest part of the county.
As the day progresses on Thursday, through Thursday night and into Friday morning, something unusual will likely happen (actually, this whole event is somewhat unusual). Another upper-level disturbance along the jet stream will drop southeast into the cut-off low. As it does this, it will create what is called a “Fujiwara” effect where this new disturbance “dumbells” with the original disturbance (now cut-off). This will do two things; 1) it will pull the surface low a bit back to the northwest, closer to the coast and 2) the new disturbance will enhance the snowfall along the northwest margin of the precipitation shield. As a result of all this strangeness we are most likely to see accumulating snowfall during this period, especially since the snow will mostly be falling overnight when there is no incoming radiation from the sun (can pass through clouds during the day, especially this time of year) and temperatures will be colder, probably in the 20s. The most likely snowfall accumulation during this period looks like 3-6″, with the highest amounts in the elevated terrain to the east.
Once the cut-off incorporates this new disturbance it will help swing the whole mess to the east and allow a milder ridge, with associated surface high pressure to build in from the west for the weekend. As a result, we are likely to see abundant sunshine for Saturday and probably most of Sunday with much milder temperatures in the 40s. This should help melt whatever snowfall we get in the next several days.
Tuesday Night
Increasing cloudiness. There is the chance of a snow shower after midnight, predominantly over the elevated terrain to the east. Probability of precipitation 30%. Nothing more than a dusting.
Temperatures will fall to the upper 20s in most locations, near 30 in the lower elevations of South County and mid 20s over the elevated terrain before midnight and then hold steady for the remainder of the night.
Light northeast winds this evening, increasing to 10-15 mph by morning.
Wednesday
Mostly cloudy with a chance of snow showers, snow showers likely over the elevated terrain to the east, particularly during the middle part of the day. Probability of precipitation 50%, 70% over the elevated terrain to the east. Accumulations, nothing more than a dusting in most locations, up to 1″ over the elevated terrain to the east.
High temperatures in the mid 30s in Pittsfield, Adams, North Adams and Williamstown, mid to upper 30s in Great Barrington and Sheffield, and low 30s over the elevated terrain and hilltowns.
Northeast winds at 10-15 mph, increasing to 15-20 mph during the afternoon. There will be some gusts over 30 mph later in the afternoon, particularly over the elevated terrain.
Wednesday Night
Overcast with a steady light snow likely developing over southern portions of the county, particularly the elevated southeastern terrain, after midnight. Probability of precipitation in these locations 70%. Accumulation of 1-3″ likely, with the highest amounts over the elevated southeastern terrain. There is a good chance of light snow (POP 50%) in central locations (Pittsfield) with an inch or so of accumulation possible. There is only a chance of light snow (40%) in the north, particularly the northwest where nothing more than a dusting is expected.
Low temperatures in the mid to upper 20s in most locations, mid 20s over the elevated terrain.
Northeast winds at 10-20 mph with some higher gusts.
Thursday
Overcast and cold. Any light snow will likely taper off during the morning but then return during the afternoon. Probability of precipitation 70% during the afternoon. Up to 1-2″ of snow possible by evening, particularly over the elevated terrain.
High temperatures in the low 30s in Pittsfield, Adams, North Adams, and Williamstown, low to mid 30s in Great Barrington and Sheffield, upper 20s to near 30 over the elevated terrain.
Thursday Night and Friday
Light snow likely overnight and into Friday morning. Snow could be moderate at times. Snow should taper off during the morning and end by noon. Probability of precipitation 70% into Friday morning. Most likely snow accumulation from Thursday afternoon through Friday morning 3-6″ with the greatest amounts in the elevated terrain.