Note: Clicking on underlined red text provides links to various weather maps.

Summary: It will be wet and unseasonably mild this weekend as a trough in the jet stream wave pattern settles over the central to western U.S., forcing a ridge to build over the eastern U.S.. As a result, the polar front (where the polar front jet stream resides) will be stalled just to our north. A series of disturbances in the jet stream flow pattern will generate surface low pressure centers which will ride along the polar front on the eastern edge of the trough, passing to our west. The counterclockwise circulation around these lows will force mild air from our south up an over the stalled warm front (stationary front) lying just to our north. Fortunately for Berkshire County, most of the “forcing” (upward motion along the front) will be focused to our north. As a result, most of the heavy rain over the weekend will be to our north, over upstate NY, VT and NH. Flooding will likely be a major concern there as 1-3″ of rain falls on a melting snowpack that measures more than a foot in places. Icing will also be a concern to the north of the front as warm air aloft overrides cold air at the surface in the Champlain Valley, northeastern NY and northern VT and NH.

Flooding is less likely here. Although temperatures will be much milder (generally in the 40s and 50s), rainfall totals should not be as heavy, 0.50″ or less in most locations. Northernmost portions of the county will likely see more rainfall but totals should still remain 1″ at most. One caveat…although the heavy rain should stay to our north, there will be a well-defined line between heavy rain to the north and light rain to the south, so it would not take much of a southward shift in the position of the front for us to be in the heavy rainfall band.

The first low to ride along the front is passing by to our northwest this afternoon. Upward motion along the warm front has generated a band of showers, but this rain has become heavier to our north. We will continue to have a low overcast tonight but with nothing more than a few light showers, sprinkles and showers. Patchy fog will likely develop as milder air moves over the cold snow pack. Another weak low will move along the front just to our north and west Saturday afternoon and evening. Occasional rain and showers are likely as this low moves by, with the heaviest rain falling in North County. As this low moves by, it will push the front even further north and allow even warmer air to infiltrate the county with temperatures holding well into the 40s overnight Saturday. A stronger low pressure system will develop over the Ohio Valley Saturday night and pass to our northwest on Sunday. This will force unseasonably mild air into the county for Sunday. Temperatures will be at near record levels on Sunday, approaching 60 degrees (the record for the date for Pittsfield is 59), with temperatures well into the 70s over the Carolinas and Virginia. Most of the heavy rainfall will to our north, although we will likely see some showers here, predominantly from the early morning hours and into early afternoon on Sunday.

This last surface low will finally drag its cold front slowly through the county Sunday afternoon into Monday as the trough finally shifts east and temperatures drop slowly through Monday. The arctic air will filter in on Tuesday (Christmas eve) on strong northwesterly winds and there may even be a few lake-effect snow showers. Christmas Day looks to have quite a bit of sunshine and much lighter winds as surface high pressure builds directly over us. It will be quite cold, however. There is a chance that a coastal storm could develop late next week but it is much too early to guess whether we will be impacted and what type of precipitation the storm might bring if it does develop and impact us.

Friday Night

Mostly cloudy with scattered light showers possible, predominantly before midnight. Patchy fog likely developing after midnight. Probability of precipitation 40%, 50% in North County. Likely rainfall totals 0.05″ or less.

Temperatures holding steady in the mid to upper 30s.

South-southwesterly winds at 5-10 mph.

Saturday

Overcast and mild with periods of rain and showers likely. Patchy fog in places. Showers will fall mainly during the afternoon and will increase in coverage and intensity as the afternoon progresses. Probability of precipitation 60% in South County, 80% in central Berkshire and 90% in North County. Likely rainfall totals less than 0.10″ in South County, around 0.10″ in central Berkshire and 0.10″ to 0.25″ in North County.

High temperatures in the mid to upper 40s in Pittsfield; mid 40s in Adams, NorthAdams and Williamstown; upper 40s in Lee and Stockbridge; near 50 in Great Barrington and Sheffield and; mid 40s over the elevated terrain.

South-southwesterly winds at 5-10 mph.

Saturday Night

Occasional rain. Patchy fog developing. Probability of precipitation near 100% but only 90% in South County. Likely rainfall totals 0.10″ to 0.25″ in South County, 0.25 to 0.50″ in central Berkshire and 0.50″ to 0.75″ in North County.

Temperatures holding steady in the mid to upper 40s during the evening, then rising slowly after midnight. By daybreak temperatures should reach near 50 to the low 50s in most locations.

South-southwesterly winds at 5-10 mph in the evening, increasing to 10-15 mph by daybreak.

Sunday

Any steadier rain or showers should end early, then remaining overcast, breezy and unseasonably warm with a few scattered light showers and sprinkles.

High temperatures near 60 in Pittsfield, Adams, NorthAdams and Williamstown, Lee and Stockbridge; low 60s in Great Barrington and Sheffield and: mid to upper 50s over the elevated terrain.

South-southwesterly winds at 10-15 mph with occasional gusts to 25 mph.