Summary: A low amplitude ripple has developed along the polar front, which passed to our south yesterday. A very weak surface low pressure system and associated upward motion in the atmosphere has developed in response to this low amplitude wave in the jet stream, as this wave creates divergence in the wind flow aloft. As the low moves by to our south and out to sea, Berkshire County will see some intermittent light snow develop this afternoon and into this evening. Off and on snow showers will continue through the night as the low pulls away and the west-northwesterly winds behind it (counterclockwise flow around low pressure) begin to generate some lake-effect snow showers. So, essentially, we will see a combination of what we call “system” snow and “lake-effect” snow overnight tonight. All of this snow, no matter what is causing it (and no matter what you call it) will not amount to much in the way of accumulations. Most locations will see accumulations in the 1-2″ range although there could be 3″ in a few spots in the elevated terrain to the east.

Once the surface low pulls away, the northwest flow around the low will pull down even colder arctic air out of Canada for Tuesday through Thursday, the coldest air of the season. High temperatures will probably hold steady in the low teens on Tuesday and will likely not get out of the single digits on Wednesday. Overnight lows will be near zero both Tuesday and Wednesday night. How frigid overnight lows get depends on how much clearing we get and how light the winds get. Right now Wednesday night looks like the coldest night with lows probably below zero. There will be a fairly persistent west-northwesterly breeze so it will feel even more frigid with wind chill temperatures below zero and as much as 10-20 degrees below zero at times.

We still look on track to get a “moderate” snowstorm late Friday into Saturday. At this point it looks like about 3-6″. The wave in the jet stream generating the surface low looks somewhat positively tilted (with a “forward” facing tilt) and progressive (moving quickly) so it looks like a fast moving storm without particularly heavy snow.

Monday Afternoon and Night

Overcast with intermittent light snow developing late this afternoon and continuing through this evening. The snow will become even more intermittent and showery after midnight. Probability of precipitation 90%. Accumulations most likely in the 1-2″ range for most locations although there could be up to 3″ in a few spots over the elevated terrain to the east.

Temperatures will hold near 20 during the evening and then drop after midnight. Low temperatures by morning will be in the low teens in Pittsfield, Adams, North Adams and Williamstown, mid teens in Great Barrington and Sheffield, and upper single digits in the elevated terrain and hilltowns.

Light southerly winds this evening, shifting to west-northwesterly just before midnight and increasing to 10-15 mph after midnight. Winds will increase to 15-20 mph over the elevated terrain with some gusts over 30 mph.

Tuesday

There will be variable amounts of clouds, depending on where the lake-effect snow shower bands set up. On average it will be partly sunny (50-75% cloud cover) to mostly cloudy (75-95%). Skies may clear a bit late in the afternoon. There is a good chance of a snow shower. Probability of precipitation 50% (probability of snow in any given location). Some locations may receive a dusting.

Temperatures will not rise much and it will feel even colder with a stiff west-northwesterly breeze. High temperature in the low to mid teens in Pittsfield, Adams, North Adams and Williamstown, mid teen in Great Barrington and Sheffield, and near 10 in the elevated terrain and hilltowns. Wind chill temperatures will be in the single digits below zero at times.

West-northwesterly winds at 10-15 mph, 15-20 mph over the elevated terrain with higher gusts.

Tuesday Night

Becoming partly cloudy. There is still the chance of a snow shower, mostly during the evening. Probability of precipitation 30%.

Low temperatures will fall to near zero in most locations, with 0 to -5 degrees in the elevated terrain and hilltowns. Wind chill temperatures -10 to -15 at times.

West-northwesterly winds will lighten up a bit and will average around 5-10 mph in most locations.

Wednesday

Partly to mostly cloudy, breezy and frigid.

High temperature in the upper single digits in Pittsfield, Adams, North Adams and Williamstown, near 10 in Great Barrington and Sheffield, and low to mid single digits in the elevated terrain and hilltowns. Wind chill temperatures from -10 to -20 at times.

West-northwesterly winds at 10-15 mph, 15-20 mph in the elevated terrain with higher gusts.