By Joseph E. Becker, Special to The County
Wednesday–Friday
The Saint John Valley begins Wednesday with generally pleasant early-September weather before conditions turn considerably wetter. High pressure moving into the Canadian Maritimes will maintain dry conditions through much of the day, with morning fog giving way to a mixture of sunshine and clouds. Meanwhile, low pressure and an associated frontal system approaching from Quebec will draw increasing moisture into northern Maine Wednesday night. Clouds will thicken, with rain developing after midnight.
Thursday looks like the wettest day of the forecast period. A developing area of low pressure moving along the frontal boundary will bring widespread rain to northern Maine, accompanied by cool temperatures and a southeasterly breeze. Rainfall from Wednesday night into Saturday should generally total 0.50–0.75 inch, with localized amounts around 1 inch possible. Given recent dry conditions, the rain should be beneficial, and flooding is not expected.
Steadier rain will diminish Thursday night as the surface low moves toward the Maritimes, but the larger upper-level system will be slower to depart. Friday will therefore remain unsettled, with showers most numerous across northern Maine. A few afternoon thunderstorms are also possible before the system gradually begins pulling away.
Saturday–Tuesday
The departing storm system will continue to influence the Valley Saturday. A disturbance rotating around the low over the Maritimes will maintain scattered showers, while brisk northerly winds add to the cool early-September feel. Conditions should gradually improve as the system moves farther east.
Drier air arrives Saturday night, setting the stage for a substantially better Sunday with partly to mostly sunny skies and seasonably cool temperatures. High pressure should then provide favorable weather for Labor Day, with plenty of sunshine, lighter winds and temperatures recovering into the lower 70s.
The next weather system begins approaching from the west Monday night into Tuesday. Clouds may increase, but current indications favor much of Tuesday remaining dry and seasonable. The timing of the approaching frontal system remains uncertain, so the potential for showers Tuesday will depend on how quickly the system advances into northern Maine.
Looking Ahead: September 9–14
The latest Climate Prediction Center outlook indicates equal chances of above-, near-, or below-normal temperatures and precipitation across northern Maine during the period. This reflects uncertainty in the developing weather pattern rather than a forecast specifically favoring normal conditions. Across the Saint John Valley, early to mid-September climatology generally features daytime highs in the mid-60s and overnight lows in the lower to middle 40s, with temperatures gradually trending downward as September progresses.
Daily Forecast Summary
Wednesday: Mostly sunny during the morning, becoming partly sunny during the afternoon. Patchy morning fog. Highs in the lower 70s. Southeast winds 5–10 mph.
Wednesday Night: Mostly cloudy with a 50% chance of rain after midnight. Lows in the lower 50s. Southeast winds 5–10 mph, with gusts up to 20 mph.
Thursday: Patchy morning fog, followed by widespread rain. Cool, with highs in the lower 60s. Southeast winds 5–10 mph, gusting up to 20 mph. Chance of rain 90%.
Thursday Night: Cloudy. Rain likely during the evening, becoming more showery after midnight. Lows in the lower 50s. Southeast winds 5–10 mph. Chance of rain 70%.
Friday: Showers likely during the morning, becoming more numerous during the afternoon with a slight chance of thunderstorms. Highs in the upper 60s. North winds 5–10 mph. Chance of rain 80%.
Friday Night: Showers with a slight chance of thunderstorms during the evening, with showers remaining likely overnight. Lows in the upper 40s. Chance of rain 80%.
Saturday: Mostly cloudy during the morning, becoming partly sunny. A 50% chance of showers. Highs in the mid-60s.
Saturday Night: Partly cloudy with a 40% chance of evening showers. Lows in the lower 40s.
Sunday: Mostly sunny during the morning, becoming partly sunny during the afternoon. Highs in the upper 60s.
Sunday Night: Mostly clear and cool. Lows in the lower 40s.
Labor Day: Mostly sunny and milder. Highs in the lower 70s.
Monday Night: Partly cloudy. Lows in the mid-40s.
Tuesday: Partly sunny with highs in the upper 60s.
Tuesday Night: Partly cloudy to mostly cloudy and seasonably cool. Lows generally in the 40s. A shower may become possible depending on the timing of the next approaching frontal system.
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.
