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Thu. Sep. 3 – Sat. Sep. 5
A slow-moving low pressure system will keep northern Maine unsettled through Saturday. An upper-level low over Quebec and an associated occluded front will move into Maine today, while secondary low pressure develops and tracks toward the Gulf of Maine tonight before moving into the Maritimes Friday. The upper-level system will move across the region more slowly, allowing clouds and showers to linger after the steadier rain ends.

For the Saint John Valley, increasing southeast flow will draw deeper moisture into the region today, producing widespread rain, areas of fog, and low clouds. Rainfall through the event should generally total 0.75 to 1.50 inches, although the Valley should remain northwest of the heaviest rainfall expected farther into New Brunswick. The atmosphere will remain relatively stable today, favoring steady rain rather than thunderstorms. Colder air aloft will make precipitation more showery Friday and Saturday before conditions gradually improve.

The primary forecast uncertainty concerns how quickly the upper low moves into the Maritimes Friday and Saturday. A slower evolution would maintain clouds and showers longer, while a faster departure would allow more substantial clearing Saturday.

Thursday: Cloudy, cool, and wet conditions will dominate as an occluded front and developing low pressure move through the region. Rain will become widespread during the morning and continue through much of the day, with periods of moderate rain possible. Areas of fog and low clouds will also develop. Temperatures will struggle to rise beyond the lower 60s, with southeast winds increasing as the system approaches. Rain continues tonight, with temperatures holding in the mid- to upper 50s.

Friday: Steady rain will gradually become more intermittent and showery as the surface low moves toward the Maritimes. Considerable cloud cover will persist, although some brighter intervals may allow temperatures to recover into the mid to upper 60s. Colder air aloft could support locally heavier afternoon showers, but widespread thunderstorms are not expected. Showers become less numerous Friday night, with lows in the lower 50s.

Saturday: The lingering upper-level low will keep conditions somewhat unsettled, with mostly cloudy skies and scattered showers, especially earlier in the day. Shower coverage should gradually decrease as the system pulls farther east. Highs will reach the lower to mid-60s. Drier conditions should begin developing Saturday night, with lows falling into the mid- to upper 40s.

Sun. Sep. 6 - Wed. Sep. 9

A quieter but still changeable pattern is expected from Sunday through Wednesday. The upper-level low responsible for the late-week unsettled weather will gradually drift east through the Maritimes Sunday into Monday while high pressure builds into northern New England, bringing drier conditions and increasing sunshine.

An upper-level trough will cross the region later Monday into Tuesday, bringing a chance of scattered showers, mainly after midnight Monday night and continuing into part of Tuesday. Cooler high pressure southeast of James Bay will then build into the region behind the departing system, bringing another period of drier and cooler weather. By Wednesday, another low-pressure system will approach from the west, increasing clouds and eventually bringing another chance for showers. Forecast confidence decreases by midweek, particularly regarding the timing of this system and how much moisture accompanies it.

Sunday: A much-improved day is expected across Fort Kent and the Saint John Valley as the departing upper low moves farther into the Maritimes. Skies should range from mostly sunny to partly cloudy, with dry conditions and highs in the mid to upper 60s. This will be close to early-September normals and noticeably brighter than Friday and Saturday. Sunday night should be partly cloudy to mostly clear and cool, with lows generally in the lower to mid-40s. Patchy river-valley fog may develop late where winds become light.

Labor Day: High pressure will provide a pleasant holiday across northern Maine. Partly to mostly sunny skies and a moderating air mass should allow temperatures to rise into the lower to mid-70s, several degrees above normal, while humidity remains comfortable. Clouds may begin increasing Monday night as the next weak front or trough approaches from the west. Overnight lows should range from the upper 40s to around 50°F.

Tuesday: A weak frontal passage should bring cooler air back into Fort Kent and the Saint John Valley. Current guidance favors a mainly dry day with clouds gradually decreasing, although the timing of the front remains somewhat uncertain. Highs should fall back into the lower to mid-60s. Tuesday night should be partly cloudy and cool, with lows generally in the lower to mid-40s.

Wednesday: The next disturbance will begin approaching northern Maine from the west, bringing increasing cloud cover and another opportunity for showers, most likely during the afternoon or later. Highs should remain in the mid to upper 60s. Confidence is lower regarding precipitation timing and coverage this far out, and a slower-moving system could allow much of Wednesday to remain dry before shower chances increase later in the day. Wednesday night should be mostly cloudy with a continued chance of showers and lows generally in the upper 40s to around 50°F.

The latest Climate Prediction Center outlook favors near-normal temperatures and precipitation across northern Maine during the period. This suggests that temperatures averaged over the period are more likely to remain close to typical mid-September levels, while precipitation is also favored to finish near climatological norms rather than showing a distinct wet or dry tendency. 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 continuing their gradual seasonal decline.

Outlooks updated 7-9 AM weekdays & 8-10 AM weekends and holidays. Long range outlooks indicate broader temperature and precipitation trends rather than precise day-to-day forecasts.

Updated every 3-6 hours from NWS Caribou

Weather Notice: This information is based on available computer models and data and may not reflect current conditions or later forecast updates. Always visit NWS Caribou at https://www.weather.gov/car/ for the latest official watches, warnings, and advisories for northern Maine.

Credits

• Sun/Moon data from US Naval Observatory with additional information from timeanddate.com.
• NOAA Warning Banner provided by WillyWeather.com.
• Until Dec. 2026, additional Archived Weather Data from Apex Wx is at the University of Utah's MesoWest
• Apex Wx Weather Data at Synoptic Data (successor to MesoWest)
  
• Apex Wx logo by Joanna Becker ©2016 (Visit Bushi and Brush Arts Dojo)

How accurate are forecasts? On average, for the first 72 hours the accuracy is 90 percent. For days 4-7 it is 70 percent. After seven days, it is 50 percent—just good for indicating trends. On social media and other similar sites, posts that show a forecast model run a week out are just for clicks and likes, and are not considered reliable. Extended forecasts are subject to change as weather patterns evolve so should be considered guidance rather than precise predictions. Check for updated forecasts and advisories as conditions develop.