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Summary: A strong cold front, signaling the leading edge of a cold trough in the jet stream wave pattern, will pass through during the day tomorrow. The air in advance of the front is quite dry so that there will only be some scattered light rain showers as the front passes through the region. However, once the front passes, the jet stream will dip to our south, and cold air that has been building over central Canada for the past week will move in. As a result, even though the air will be modified by streaming over warmer land and Great Lakes water, temperatures will be significantly below normal, for the first time this autumn, through the end of the week.

A somewhat interesting scenario may develop on Wednesday after the front passes to our south. A disturbance in the jet stream, rotating through the base of the trough will generate a surface low pressure system along the front off the coast to our south. The global U.S. (GFS) and European (ECMWF) models have the low developing far enough off the coast so that the significant precipitation stays to the south and east of Berkshire County. However, the higher resolution U.S. (NAM) model develops the low close enough to the coast to give us significant precipitation. The way that the atmosphere is set up for this event, if we get precipitation, believe it or not, it would be an elevation type snowfall event, with mixed rain and wet snow in the valley locations with all wet snow in the elevated terrain. However, in my experience, these types of storms usually develop too far off the coast to impact us. Therefore, at this point, I find the GFS and ECMWF scenarios more realistic and I suspect we will get nothing more than light amounts of wet snow at most on Wednesday (sorry snow lovers). I will update this tomorrow afternoon.

One thing that is fairly certain is that we will have much colder weather than we have become used to with high temperatures in the 40s at best and lows in the 20s Wednesday through Friday. There may be a bit of moderation over the weekend as the jet stream wave pattern becomes less amplified and the coldest air shifts to our north and east.

Monday Night

Mostly clear this evening, then increasing clouds after midnight.

Low temperatures generally in the low 40s, near 40 over the elevated terrain.

South-southwesterly winds at 5-10 mph.

Tuesday

Mostly cloudy with the chance of a few scattered, light showers through mid-afternoon. The best chance for a shower is during the early afternoon. Skies will clear during the mid to late afternoon hours. Probability of precipitation 40%. Any rainfall should be 0.05″ or less.

High temperatures in the low to mid 50s in Pittsfield, North Adams, Adams and Williamstown; mid 50s in Lee, Stockbridge, Great Barrington and Sheffield and; upper 40s to near 50 over the elevated terrain and hilltowns, depending on elevation.

Southwesterly winds at 10-15 mph, shifting to northwesterly mid-afternoon.

Tuesday Night

Partly cloudy and much colder. Clouds increasing toward daybreak.

Low temperatures in the low 30s in most locations, low to mid 30s in South County and near 30 over the elevated terrain.

Light northerly winds shifting to northeasterly toward morning.

Wednesday

Overcast and unseasonably chilly. There is a good chance of a little light mixed rain and wet snow over the valley locations, possibly just rain in the lower elevations of South County, with all wet snow in the elevated terrain and hilltowns. Probability of precipitation 50% in central Berkshire, 40% in North County and 60% in South County. Any snow that falls will likely be no more than a coating in the valley locations and less than an inch over the elevated terrain. Liquid equivalent precipitation 0.10″ or less.

High temperatures near 40 in Pittsfield, North Adams, Adams and Williamstown; low 40s in Lee, Stockbridge, Great Barrington and Sheffield and; mid to upper 30s over the elevated terrain and hilltowns, depending on elevation.

Light northeasterly winds in the morning, shifting to northwesterly at 5-10 mph in the afternoon.