Southerly flow around the back side of the subtropical high pressure system (Bermuda High) off the Atlantic Coast is pumping unseasonably warm and moist air into Berkshire County. As a result, we will have very warm temperatures for this time of year through Thursday. Unfortunately, with a low sun angle as we move into mid October, all of the low-level moisture being pumped into the region will generate a persistent low-level cloud cover through the day Wednesday. There may even be enough moisture to generate some spotty drizzle or even a light shower overnight tonight and during the day on Wednesday. With dew points in the low 60s, and a cloud cover in place, there will be little radiational cooling tonight and Wednesday night and temperatures will likely not drop below 60 degrees both nights. Also, the air is so warm that despite the lack of sunshine, temperatures are likely to reach 70 degrees again on Wednesday.

Over the past few days, an elongated trough in the jet stream wave pattern over the Midwest, which is almost cut-off from the strongest upper-level westerlies located over Canada, has been propagating very slowly eastward towards the East Coast. It is generating a surface low pressure system along its eastern side, presently located in Illinois, with a trailing cold front along the eastern margin of the colder air within the trough. As this cold front plows into and lifts the the very warm, moist and unstable air in place over the Midwest and eastern U.S. it is generating a band of heavy showers and thunderstorms, some of which have been severe. By the time this front reaches us on Thursday it will have lost some of its punch. In addition, the air over us will not be nearly as unstable as it has been in the Midwest. Therefore, as the front approaches Wednesday night and then moves through on Thursday we are likely to see substantial rainfall but will not see any severe weather, although a few embedded rumbles of thunder could occur late in the day on Thursday.

The rain and showers should end Thursday evening as the front moves through. Even though it will turn “cooler” for Friday and Saturday, the air within the trough is not that cool for this time of year and, with some sunshine, temperatures will still likely be in the above normal 60s for both days. However, a mid/upper-level cold pool/disturbance will rotate into the base of the trough on Saturday, deepening it, and bringing with it much cooler temperatures. There could be a few showers as it moves through late on Saturday and then Sunday could be quite cool indeed, with temperatures not climbing out of the 40s. As the trough shifts to our east, surface high pressure will build in along the back side of the trough (the usual location) and may bring us a prolonged period of sunny, fall weather for next week.

Tuesday Night

Partly cloudy this evening, becoming overcast after midnight. There is a chance of some spotty drizzle toward daybreak.

It will be unseasonably mild with low temperatures near 60, low 60s in South County.

South-southeasterly winds at 5-10 mph.

Wednesday

Cloudy, but unseasonably warm and somewhat muggy. Spotty drizzle is possible with the chance for a widely scattered light shower or two, particularly late in the day. Probability of precipitation 40%. Likely rainfall totals 0.05″ or less.

High temperatures near 70 in Pittsfield, Lee, Stockbridge, Adams, North Adams and Williamstown; low 70s in Great Barrington and Sheffield and; upper 60s over the elevated terrain.

Southeasterly winds at 5-15 mph.

Wednesday Night

Cloudy and unseasonably mild and humid. Showers likely developing during the evening with off and on showers after midnight. Probability of precipitation 90%. Likely rainfall totals between 0.25″ and 0.50″.

Low temperatures in the low to mid 60s.

Southeasterly winds at 5-10 mph.

Thursday

Cloudy and rainy, but still warm and muggy, with periods of rain and showers, heavy at times. The heaviest showers are most likely late in the day, and there may even be a few embedded rumbles of thunder. Probability of precipitation near 100%. Likely additional rainfall totals 0.50″ to 0.75″. Totals could be higher over the elevated terrain to the east.

High temperatures in the upper 60s in most locations; mid to upper 60s over the elevated terrain.

East-southeasterly winds at 5-15 mph.