Wednesday-Friday
A cold, frosty start Wednesday will mark the beginning of another transition in the St. John Valley. High pressure responsible for the chilly morning will shift east of Maine, allowing south to southwest winds to draw increasing moisture into northern Aroostook County. Clouds will thicken through the day, with scattered light rain developing during the afternoon.
Rain will become more widespread Wednesday night as low pressure stalls northwest of Maine and its associated frontal system approaches.
Thursday will be the wettest and mildest day of the three. Showers will be likely as the cold front crosses northern Maine, although rainfall totals should remain modest and provide little meaningful relief from ongoing dry conditions. Some instability may develop during the afternoon, particularly across northern areas, allowing an isolated thunderstorm to accompany a line of showers. Small hail could occur with a stronger shower, but severe weather is not expected.
Cooler west to northwest flow will return behind the front Thursday night. An upper-level disturbance lingering over the region will keep Friday somewhat unsettled, with considerable cloud cover and scattered showers possible. West winds will become breezy, adding to the cooler feel as afternoon temperatures retreat.
High pressure will begin building toward northern Maine Friday night, bringing clearing skies and temperatures falling toward freezing. Frost will again become a concern across the Valley by Saturday morning.
Saturday-Tuesday
Saturday begins frosty but should develop into a quiet, cool autumn day as high pressure becomes established across northern New England. Mostly sunny skies are expected, although the cool Canadian air mass will keep afternoon temperatures near 50°F. Winds will gradually diminish, setting the stage for another cold Saturday night. Sheltered portions of the Saint John Valley could again fall to around freezing with widespread frost possible.
A pronounced change arrives Sunday as the high moves east and southerly return flow develops. Following the chilly morning, sunshine and warmer air should allow temperatures to rebound into the upper 50s to lower 60s. Sunday currently appears to offer the most favorable weather of the period for outdoor activities. Clouds will increase Sunday night as moisture begins returning ahead of the next system, with rain becoming possible toward Monday morning.
Monday turns more unsettled as a frontal system approaches northern Maine. Rain chances increase during the day while temperatures remain relatively mild for mid-October. The system may remain influential Monday night into Tuesday, with additional periods of rain possible as temperatures begin trending cooler. The timing and progression of the system remain uncertain this far out, so Tuesday’s shower coverage will depend on how quickly the front moves through northern Maine.
Looking Ahead: October 14-20
The Climate Prediction Center favors below-normal temperatures and above-normal precipitation across northern Maine for October 14-20. Ensemble guidance differs considerably on the details of the week-two pattern, lowering confidence, but the broader signal supports opportunities for cooler Canadian air along with a relatively active precipitation pattern. By mid-October, typical St. John Valley daytime highs are generally in the upper 40s to lower 50s, with overnight lows in the lower to middle 30s.
Daily Forecast Summary
Wednesday: Mostly cloudy after widespread morning frost. Rain becomes increasingly possible during the afternoon, with chances around 50%. Highs in the lower 50s. Southwest winds 5-10 mph, occasionally gusting around 20 mph.
Wednesday Night: Cloudy with rain becoming likely, particularly after midnight. Rain chance around 60%. Lows in the lower 40s with south winds 5-10 mph.
Thursday: Cloudy with showers likely and an isolated afternoon thunderstorm possible across northern areas. Rain chance around 70%. Highs in the middle 50s with southwest winds 5-10 mph.
Thursday Night: A chance of evening showers, then mostly cloudy with only a slight chance overnight. Lows around 40 degrees. Rain chance around 50% early.
Friday: Mostly cloudy and cooler with a 50% chance of showers. Highs in the upper 40s. Breezy west winds may occasionally gust around 25 mph.
Friday Night: Becoming mostly clear and colder. Lows around 30 degrees with frost developing in many locations.
Saturday: Mostly sunny after a frosty start. Highs around 50 degrees. Northwest winds gradually diminish.
Saturday Night: Mostly clear and cold with lows around 30 degrees to the lower 30s. Frost likely, particularly in sheltered valleys.
Sunday: Mostly sunny and noticeably milder. Highs in the upper 50s to lower 60s with developing southerly winds.
Sunday Night: Increasingly cloudy with a slight chance of rain developing late. Lows in the lower to middle 40s.
Monday: Partly sunny to mostly cloudy with a 40% chance of rain. Highs in the upper 50s to around 60 degrees.
Monday Night: Mostly cloudy with a 30% chance of rain. Lows in the upper 30s.
Tuesday: Partly sunny with a 30-40% chance of rain. Highs in the lower to middle 50s.
Tuesday Night: Mostly cloudy with a 40% chance of rain. Lows in the middle 30s.
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 TheCounty.me or the National Weather Service, Caribou, Maine, for the most recent weather information for the St. John Valley.
