Wednesday-Friday
A relatively mild Wednesday will begin the period before a stronger change toward cooler and windier weather arrives late in the week. A weak surface trough crossing northern Maine may produce an isolated shower early Wednesday, but most of the Saint John Valley should remain dry. Partial sunshine will help temperatures climb into the lower 70s, several degrees above normal for mid-September. Winds will shift from south to west during the afternoon and may become briefly gusty.
Clearing Wednesday night, light winds, and lingering low-level moisture will favor patchy river-valley fog toward Thursday morning. After the fog dissipates, Thursday should be a quieter transition day with partly sunny skies and temperatures returning to the mid-60s.
Clouds will increase Thursday night as low pressure crosses Quebec and an associated cold front approaches northern Maine. The deeper moisture accompanying this system should remain primarily south of the Valley, limiting rainfall locally.
The front and an upper-level trough will cross the County Friday. A few showers are possible during the morning into early afternoon, but rainfall should be light. The more noticeable feature will be the arrival of colder air and increasingly strong northwest winds. Gusts of 30–40 mph are possible during the day, particularly in exposed locations.
With trees still carrying much of their foliage, isolated tree damage or power interruptions cannot be ruled out. Showers should diminish during the afternoon, followed by clearing and a chilly Friday night as winds gradually ease.
Saturday-Tuesday
High pressure building into northern New England will bring a bright but cool start to the weekend. Saturday should feature plenty of sunshine, with temperatures struggling to reach around 60 degrees F after a chilly morning. Northwest winds will be considerably lighter than Friday, although a breeze may remain noticeable early in the day. Saturday night will turn partly cloudy and cold, with temperatures falling into the upper 30s.
The high will begin shifting east as another disturbance approaches Sunday. Clouds will increase, with scattered showers possible mainly from late morning through the afternoon. Current guidance suggests substantial dry periods, however, and uncertainty remains concerning the track and timing of the disturbance. Sunday therefore does not currently look like an all-day rain event.
Weak high pressure should return Monday, favoring mostly sunny skies and seasonably cool temperatures. Another minor disturbance or frontal feature may approach Monday night into Tuesday, producing a slight chance of showers. Much of Tuesday currently appears likely to remain dry with at least some sunshine and temperatures recovering into the lower to mid-60s.
Tuesday night should become mostly clear as the disturbance moves away. Temperatures are expected to fall into the mid- to upper 30s. If skies clear sufficiently and winds become light, sheltered portions of the Valley may again have conditions favorable for localized frost.
Looking ahead: Sept. 23–29
Normal temperatures across the Saint John Valley during this period are around 60 degrees F for daytime highs and generally in the upper 30s to lower 40s overnight, with normals continuing to decline as September progresses. Climate Prediction Center guidance favors above-normal temperatures across northern Maine, while the broader pattern favors relatively dry conditions across the interior Northeast.
Ridging over central and eastern Canada and periods of surface high pressure support the warmer, generally quieter tendency, although this represents an overall weekly pattern rather than a day-to-day forecast.
Daily Forecast Summary
Wednesday: Partly sunny with an isolated shower possible early. Highs in the lower 70s. South to southwest winds becoming west at 5-10 mph, with occasional gusts around 20 mph.
Wednesday Night: Partly cloudy with patchy valley fog developing after midnight. Lows in the lower 40s. Light northwest winds.
Thursday: Patchy morning fog, then partly sunny. Highs in the mid-60s with light winds.
Thursday Night: Partly to mostly cloudy with patchy fog and a slight chance of showers in some locations. Lows in the mid-40s. Winds light.
Friday: Patchy morning fog, then partly to mostly sunny with a chance of light showers, mainly during the morning into early afternoon. Highs in the upper 50s to around 60 degrees F. Northwest winds increasing to 15-20 mph with gusts of 30-40 mph possible.
Friday Night: Mostly clear and chilly. Lows in the mid- to upper 30s. Northwest winds remain gusty during the evening before gradually diminishing.
Saturday: Sunny and cool. Highs in the upper 50s to around 60 degrees F. Northwest winds lighter than Friday.
Saturday Night: Partly cloudy and chilly. Lows in the upper 30s.
Sunday: Increasing clouds with a 20-30% chance of showers, mainly from late morning into the afternoon. Highs in the lower 60s. Substantial dry periods remain possible.
Sunday Night: Partly cloudy with a slight chance of a shower in some locations. Lows in the upper 30s to around 40 degrees F.
Monday: Mostly sunny and seasonably cool. Highs around the lower 60s.
Monday Night: Partly cloudy with a 20% chance of showers. Lows around 40 degrees F.
Tuesday: Mostly sunny overall with a slight chance of a shower. Highs in the lower to mid-60s.
Tuesday Night: Becoming mostly clear. Lows in the mid- to upper 30s. Localized frost may be possible in sheltered valleys if winds become light.
Weather Notice: The weekly forecast, by UMFK Professor Joseph E. Becker, is based on available computer models and data and may not reflect current conditions or later forecast updates. Check The County.me or the National Weather Service Caribou, Maine for the most recent weather information for the Saint John Valley.
