Summary: Our weak, zonally oriented jet stream for the past several days has started to become more amplified with a strong, warm ridge in the jet stream developing over the western U.S. and a deep, cold trough in the jet stream plunging southward over the central and eastern U.S.. As this wave in the jet stream propagates slowly eastward as it amplifies, the cold trough will move over our region this weekend (with the leading edge of the trough represented as a cold front passage on Friday), bringing us much colder weather, particularly on Sunday, when the coldest part of the trough will be centered over our region.
It now looks as though the trough will progress a little more slowly eastward than it appeared a few days ago. As a disturbance in the jet stream rotates around the base of the trough it will create an area of divergence (diverging jet stream winds) aloft along the eastern edge of the trough. As a result, upward motion in the atmosphere will be generated and surface low pressure will develop off the Mid-Atlantic Coast during the day on Saturday. The trough will become negatively tilted (tilted backwards from the east to the west) overnight Saturday and Sunday, which will enhance the divergence aloft markedly. As a result, the surface low will deepen rapidly (we call this a “bomb”) as it is directed northeastward by the flow aloft, become a very deep low as it moves into the Canadian Maritime (970 mb in the ECMWF, 960 in the GFS! [equivalent to a Category 3 Hurricane]) Sunday evening. Fortunately (unless you are in a boat in the North Atlantic, or live in the Canadian Maritime region), this will all be happening well off the coast. Right now it looks like we will likely be on the westernmost edge of the precipitation shield from this storm. However, even though this should not be a big snowstorm for Berkshire County, I think that there is a good possibility that Berkshire County will get a few inches of accumulation overnight Saturday. In eastern New England, where they certainly don’t need it, they are likely to get more. This is NOT likely to be a repeat of last Friday, as the storm will be developing much farther away from the coastline, and much farther north along its track.
This will be a rapidly developing situation on Saturday and a change in the projected track of the low by even a small amount to the west or east, or a change in the timing of the storm development process, could result in us getting no snow at all (still a likely event) or a more significant accumulation. I will update this tomorrow afternoon.
After the low departs on Sunday, it will turn very windy and much colder as the pressure gradient force resulting from the deepening coastal low will generate strong northwest winds that will drive cold air from Canada southward over our region. After that, it looks like the jet stream wave pattern will become quite “wavy” (active) and progressive (waves in the jet stream propagating fairly rapidly eastward). As a result, there will be a series of storms moving from west to east across the country during the work week, likely effecting Berkshire County on Tuesday and again on Friday. It is unclear if these storms will bring all snow or a mixture of precipitation types. Right now I am leaning towards a mixture.
Thursday Night
Increasing cloudiness this evening, becoming mostly cloudy overnight. There is the slight chance of a snow shower or flurry, predominantly in North County. Probability of precipitation 20%. No accumulation is expected.
Temperatures will not fall much with a cloud cover and a persistent southerly breeze. Low temperatures will likely be in the upper 20s to near 30 in most locations.
Southerly winds light early, increasing to 5-10 mph by midnight and 10-15 mph by morning.
Friday
Mostly sunny and quite mild in the morning. Clouds will begin to increase late in the morning, becoming partly sunny (50-75% cloud cover) in the afternoon as the cold front moves through. Temperatures will begin to drop mid-afternoon following the cold front passage.
High temperatures will occur from late morning to early afternoon with highs near 40 in Pittsfield, near 40 to low 40s in Adams, North Adams and Williamstown, low 40s in Great Barrington and Sheffield, and mid to upper 30s over the elevated terrain and hilltowns. Temperatures will drop through the 30s over the course of the afternoon.
South-southwest winds at 10-15 mph in the morning, shifting to westerly and then diminishing somewhat over the course of the afternoon.
Friday Night
Variable amounts of cloudiness over the course of the night. It will average out partly to mostly cloudy.
Colder than Thursday night, with low temperatures near 20 to the low 20s in most locations, mid to upper teens over the elevated terrain.
Northwest winds at 5-10 mph.
Saturday
Becoming mostly cloudy to overcast. Much colder than Friday. There is a chance of snow late in the afternoon. Probability of precipitation 40%. Nothing more than a dusting to an inch or so is expected during the afternoon, although there could be more accumulation overnight (see summary above).
High temperatures in the upper 20s in Pittsfield, near 30 in Adams, North Adams and Williamstown, lower 30s in Great Barrington and Sheffield, and low to mid 20s over the elevated terrain and hilltowns (depending on elevation).
North-northwest winds at 5-10 mph.