The brief stretch of cool, dry weather comes to an end Wednesday as high pressure moves east and a strengthening low-pressure system approaches northern Maine. The day begins chilly, with frost in some of the colder locations across northern Aroostook County.
Clouds will steadily increase across the St. John Valley, while strengthening southerly winds bring milder and increasingly moist air northward. Rain develops later Wednesday and becomes widespread Wednesday night, with periods of moderate rain and gusty winds.
The associated cold front crosses the region Thursday. Steadier morning rain will become more showery before gradually tapering off, and an isolated thunderstorm cannot be ruled out. Winds will shift sharply to the west and northwest behind the front and become the day’s more noticeable weather feature. Gusts around 30-35 mph are possible, so Thursday will remain windy even after the steadier rainfall ends.
Cooler and drier air spreads into the Valley Thursday night. Friday will feel distinctly cooler as northwest flow continues, but lingering clouds will gradually give way to increasing sunshine. Winds remain somewhat brisk during the day before diminishing Friday night as high pressure begins building toward northern Maine.
Saturday-Tuesday
High pressure provides a welcome break Saturday, with mostly sunny skies, dry air, lighter winds, and temperatures rebounding into the lower 70s. The pleasant weather continues into Saturday night, although the high will begin shifting east and southerly flow will develop ahead of the next cold front approaching from Canada.
Sunday becomes warmer and increasingly unsettled. Much of the morning and early afternoon may remain dry, but clouds increase and showers become more likely later in the day. Rain chances rise further Sunday night as the front crosses northern Maine, and an isolated thunderstorm is possible. Cooler and drier west to northwest flow follows Monday, with lingering showers gradually diminishing and some sunshine returning.
The break appears relatively brief. Another frontal system approaches Tuesday, bringing increasing clouds and renewed rain chances. Much of Tuesday may remain dry before showers become more likely later in the day. Rain showers are likely Tuesday evening and may continue overnight. The timing of this frontal system remains somewhat uncertain, so how quickly rain reaches the Valley will depend on its eastward progress.
Looking Ahead: September 16-22
The latest outlook favors below-normal temperatures and above-normal precipitation across northern Maine and the St. John Valley. A developing trough over the northeastern United States should support a generally cooler pattern, although the precipitation signal remains relatively weak and does not imply rain every day. Mid-September climatology across the Valley typically features daytime highs in the mid-60s and overnight lows in the lower to middle 40s.
Daily Forecast Summary
Wednesday: Increasing clouds with rain developing later. Highs in the lower to mid-60s. South winds increasing to 10-15 mph and becoming gusty.
Wednesday Night: Widespread rain, moderate at times. Lows in the lower to mid-50s. Gusty south winds.
Thursday: Morning rain becoming scattered showers and gradually tapering off. An isolated thunderstorm is possible. Highs in the upper 60s to lower 70s. Winds shifting west to northwest with gusts around 30-35 mph.
Thursday Night: Partly cloudy, cooler, and drier. Lows in the mid- to upper 40s. West to northwest winds gradually diminishing.
Friday: Lingering clouds giving way to increasing sunshine. Distinctly cooler, with highs in the upper 50s to lower 60s. Breezy northwest winds.
Friday Night: Mostly clear and cool. Lows in the lower 40s, with locally colder conditions possible in sheltered locations. Winds diminishing.
Saturday: Mostly sunny, dry, and pleasant. Highs in the lower 70s. Relatively light winds.
Saturday Night: Partly cloudy. Lows in the upper 40s to around 50 degrees F with light winds.
Sunday: Increasing clouds with showers developing later. Highs in the lower to mid-70s. Southerly winds becoming more noticeable.
Sunday Night: Showers likely with an isolated thunderstorm possible. Lows in the lower to mid-50s.
Monday: Lingering showers, especially earlier, followed by some breaks of sunshine. Highs in the mid- to upper 60s. West to northwest winds.
Monday Night: Partly cloudy and cooler with diminishing shower chances. Lows generally in the mid-40s.
Tuesday: Increasing clouds with rain showers becoming more likely later in the day. Highs in the mid-60s.
Tuesday Night: Mostly cloudy with rain showers likely, particularly during the evening. Around a 60% chance of rain during the evening, decreasing to around 50% overnight. Lows in the lower 50s.
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.
