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Summary: The change in the jet stream wave pattern discussed yesterday appears to be taking hold and it looks like, after one more mild day temperatures will become more seasonable on Friday and Saturday, then slightly below normal from Sunday through Tuesday and then quite cool mid to late week next week. The drop in temperatures will occur in steps as a series of cold fronts move through the region, each one generated by disturbances rotating through the base of the trough. As each subsequent disturbance rotates through, it will drive the cold trough further to the south and east, moving us closer to the core of the cold Canadian air.

The threat for showers tonight has decreased since yesterdays forecast with only the chance of a few scattered light showers or sprinkles overnight as the southern branch of the jet stream begins to settle south and east, pushing a weakening cool front over us. The cool front will weaken and stall over us on Thursday, providing fairly cloudy but dry conditions. A fairly vigorous disturbance in the jet stream will generate surface low pressure which will move along the cool front and directly over the region Thursday night. A several hour period of rain, moderate at times, will accompany the passage of this low pressure system, beginning mid to late evening and continuing into the early morning hours. Skies should clear for Friday, with a fresh northwest breeze making it feel a bit more like mid October, although temperatures will remain slightly above normal.

Over the weekend, the jet stream wave pattern will further its amplification. As the cold trough dives south, the northern and southern branches of the jet stream will begin to merge to our north and west.  Saturday will be a transitional day, with partly cloudy skies and seasonable temperatures as weak surface high pressure develops in advance of the trough. A disturbance in the jet stream along the southeastern edge of the trough will develop as the two branches merge. This will generate surface low pressure in southern Quebec. As the low moves north and east it will drag its trailing cold front over us Saturday night. There is only a chance of scattered showers with this cold front passage but significantly cooler air will filter in behind the front and temperatures on Sunday may have trouble making it past the low 50s.

Wednesday Night

Mostly cloudy. There is a good chance of a few scattered light showers or sprinkles. Probability of precipitation 50%. Rainfall totals will likely be .05″ or less.

It will be fairly mild, with low temperatures in the low 50s.

Light southerly winds shifting to southwesterly after midnight.

Thursday

Partly sunny and mild.

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

Westerly winds at 5-10 mph.

Thursday Night

Rain, moderate at times, developing in the mid to late evening and ending in the early morning hours. Probability of precipitation 90%. Most likely rainfall totals around 0.50″.

Low temperatures generally near 50, mid to upper 40s over the elevated terrain.

South winds at 5-10 mph in the evening, increasing to 10-15 mph and shifting to west-northwesterly in the early morning hours.

Friday

Partly cloudy, breezy and a bit cooler.

High temperatures in the low 60s in Pittsfield, North Adams, Adams and Williamstown; low to mid 60s in Lee, Stockbridge, Great Barrington and Sheffield and; mid to upper 50s over the elevated terrain and hilltowns, depending on elevation.

West-northwesterly winds at 10-15 mph in the lower elevations, 15-20 mph over the elevated terrain, with gusts 25-30 mph at times, particularly over the elevated terrain.

Saturday and Sunday

Partly cloudy skies both days. There is a chance of a shower with the passage of a cold front overnight Saturday. It will be considerably cooler on Sunday than Saturday with high temperatures averaging in the low 60s on Saturday and low 50s on Sunday.