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Summary: We have been basking in unusually mild and dry autumn weather for the past several days as the jet stream remains weak and located to our north. Presently the jet stream is “split” with a northern branch located over central Canada and a southern branch over the Great Plains and Midwest. We are under the influence of an unseasonably mild air mass, which is actually part of the semi-permanent subtropical high pressure belt (Bermuda High) to the south of both these branches. However, the mid to long range computer models are suggesting the jet stream wave pattern is about to undergo a fairly pronounced change, which could ultimately result in a change to more seasonable temperatures Friday through Sunday, transitioning to below normal temperatures for early next week. In fact, if the models are to be believed this far in advance, we may have below normal temperatures mid to late next week with high temperatures only in the 40s.

The scenario looks like this…..relatively cold air is beginning to build over north-central Canada. As the jet stream wave pattern amplifies and the two branches merge over the next several days a ridge will build over western North America and a deep trough will begin to dig south over central and eastern Canada and eventually the Midwest and Northeast U.S. This will permit the cold Canadian air to plunge southward.

As this jet stream pattern transitions, we will be impacted by a few periods of rain and showers over the next few days as the two branches pass southeastward and merge over our region. More specifically, the southern branch of the jet stream will push a cool front through the region Wednesday night into Thursday morning, accompanied by a a few showers . It will then stall over the region, allowing a disturbance in the jet stream to generate a weak low pressure system that will likely move through with more substantial rain on Thursday night. Weak high pressure should then build in over the weekend as the two jet stream branches finally merge and the jet stream “stretches out” and settles over the eastern U.S., resulting in a dry weekend with seasonably cool temperatures.

Tuesday Night

Mostly cloudy this evening, then clearing skies overnight. Becoming mostly cloudy again toward morning.

Low temperatures in the mid 40s.

Calm winds.

Wednesday

It will be variably cloudy but there will be considerably more clouds than sun in most locations.

It will be unseasonably mild, with high temperatures in the mid to upper 60s in Pittsfield, North Adams, Adams and Williamstown; upper 60s to near 70 in Lee, Stockbridge, Great Barrington and Sheffield and; low to mid 60s over the elevated terrain and hilltowns.

Southeasterly winds at 5-10 mph in the morning, shifting to southerly and increasing to 8-12 mph in the afternoon.

Wednesday Night

Mostly cloudy and mild. Scattered showers are likely after midnight. Probability of precipitation 60%. Rainfall totals 0.10″ or less.

Low temperatures in the mid 50s, low 50s over the elevated terrain.

Southerly winds at 5-10 mph, shifting to westerly near daybreak.

Thursday

Chance of a few lingering light showers early. Remaining mostly cloudy through mid to late morning, then becoming partly cloudy.

Remaining mild, with high temperatures in the mid 60s in Pittsfield, North Adams, Adams and Williamstown; mid to upper 60s in Lee, Stockbridge, Great Barrington and Sheffield and; near 60 to low 60s over the elevated terrain and hilltowns.

West-northwesterly winds at 5-10 mph.

Thursday Night

Increasing cloudiness in the evening. A period of rain, moderate at times, likely developing after midnight. Probability of precipitation 70%. Rainfall totals between 0.25″ and 0.50″. Low temperatures in the mid 40s.

Friday

Mostly cloudy early, then decreasing clouds. Partly cloudy during the afternoon. Slightly cooler, although still pleasant, with high temperatures averaging near 60 to the low 60s.