Apex Wx

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Monday, September 14 – Wednesday, September 16

Overview: A cold front will move through northern Maine and the Saint John Valley Monday morning, bringing scattered showers before drier air arrives from the west. Behind the front, northwest winds will strengthen and temperatures will remain cool for mid-September. Gusts of 25–35 mph are possible during the afternoon as colder air moves into the region and stronger winds aloft mix down to the surface.

High pressure will build into northern New England Monday night, allowing skies to clear and winds to diminish. This will set up a chilly night, with temperatures falling into the upper 30s to around 40°F across much of the Valley. Patchy frost is possible in sheltered locations, along with some late-night river-valley fog.

Tuesday will be dry and quieter as high pressure settles across the region. As the high shifts east, winds will turn southerly and temperatures will begin to recover. By Wednesday, southwest flow will bring a much warmer air mass into northern Maine, with highs reaching highs reaching the lower 70s. The next frontal system should remain west of the area through Wednesday, so dry weather is expected to continue into midweek.

Monday: Scattered showers will accompany the cold front across Fort Kent and the Saint John Valley early this morning, then taper from west to east by mid-morning as the front and upper trough move into New Brunswick. Clouds will gradually break, but the more noticeable change will be the arrival of cooler air and stronger northwest winds. Highs will be mainly in the mid- to upper 50s, with northwest winds of 10–15 mph gusting 25–35 mph through much of the afternoon. Skies will clear Monday evening as high pressure builds in and winds become light. Lows will fall into the upper 30s to around 40°F in much of the Valley, with lower to mid-30s possible in colder sheltered locations. Patchy frost and some river-valley fog are possible toward morning.

Tuesday: Any early valley fog or frost will dissipate after sunrise, followed by a dry and increasingly pleasant day as high pressure settles across northern New England. Sunshine will dominate much of the day, although clouds may begin increasing later in the afternoon as the high shifts east and southerly flow develops. Temperatures will recover into the mid-60s, with light south winds generally around 5–10 mph. Tuesday night will be considerably milder than Monday night, with periods of clouds and lows in the upper 40s to around 50°F. No precipitation is expected.

Wednesday: A warmer southwest flow will become established as high pressure moves farther east, bringing a substantial temperature rebound to the Saint John Valley. Wednesday should be mainly sunny to partly cloudy and dry, with highs in the lower 70s, well above Monday's readings and several degrees above normal for mid-September. Winds will remain relatively light, generally from the southwest to west. Wednesday evening and night will stay dry with mostly clear skies as the next frontal system remains to the west. Lows will settle into the lower 40s, with somewhat colder readings possible in sheltered terrain.

Thursday, September 17 – Sunday, September 20

Overview:  After the warmer weather Wednesday, a Canadian low and associated cold front will move toward northern Maine on Thursday. Clouds will increase and showers will become more likely as the front crosses the Valley. Current NWS Caribou guidance suggests this will be a relatively weak system, with intermittent showers rather than a prolonged rain. The deeper moisture associated with the front should remain focused farther south, so rainfall in northern Maine is expected to be limited.

Cooler and drier air will move in behind the front Friday as winds turn west to northwest. Any lingering showers should end, followed by increasing sunshine and temperatures returning closer to seasonal levels.

High pressure should become more influential over the weekend, bringing mainly dry and seasonably cool weather Saturday and Sunday. Nights will turn chilly again, especially in sheltered areas where clear skies and light winds may allow temperatures to fall into the upper 30s to around 40°F. Patchy valley fog, and possibly localized frost in the coldest spots, may develop during the late-night and early-morning hours.

Thursday: Clouds will increase as the cold front approaches the Saint John Valley, with showers becoming possible during the day and continuing into Thursday night. Current NWS guidance favors a fairly weak frontal passage, so precipitation should be intermittent rather than an all-day rain. Highs will generally reach the mid-60s, with somewhat warmer readings possible toward Van Buren and eastern portions of the Valley. Winds should remain relatively light. Thursday night stays mostly cloudy with a continued chance of showers as the front moves through, with lows generally in the mid-40s.

Friday: Any lingering showers should diminish as the front moves east and drier air begins spreading into northern Maine. Clouds will give way to increasing breaks of sunshine, with highs mainly in the lower to mid-60s. Winds will remain fairly light, becoming west to northwest as the post-frontal air mass settles in. Friday night should turn mostly clear and cooler, with lows falling into the lower 40s, and some colder sheltered locations possibly reaching the upper 30s. Patchy valley fog may develop late where winds become calm.

Saturday: High pressure should provide a dry and seasonably cool day with mostly sunny skies. Temperatures will likely remain in the lower 60s, with light winds and relatively low humidity. Saturday night should remain mostly clear with lows in the upper 30s to around 40°F. Colder sheltered locations could fall a few degrees lower, so localized frost cannot yet be ruled out if winds fully subside.

Sunday: The weekend should remain predominantly dry as high pressure continues to influence northern Maine. Sunshine may mix with some clouds during the day, with temperatures likely holding in the upper 50s to around 60°F. Winds should remain light. Sunday night currently appears mainly dry and cool, with lows again in the upper 30s to near 40°F, although confidence is lower by this point regarding cloud cover and the timing of the next upstream disturbance.

Long Range: Monday, September 21 – Sunday, September 27

CPC leans toward above-normal temperatures for northern Maine, with the Saint John Valley near the eastern edge of that warmer signal, while precipitation is in the equal-chances category. A trough over the Northeast early in the period is expected to weaken as ridging advances east from central Canada. Typical late-September conditions in the Valley feature daytime highs in the low to mid-60s and overnight lows in the lower to mid-40s.

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

Apex Wx forecasts are based on available observations, computer model guidance, and other meteorological data. Conditions and forecast guidance can change, and information displayed here may not reflect the latest official forecast or warning information. Always visit NWS Caribou for the latest official forecasts, watches, warnings, and advisories for northern Maine.

Apex Wx is a private weather information service unaffiliated with NOAA or the National Weather Service and operated by Joseph Becker, PhD. Dr. Becker earned a Certificate in Weather Forecasting from Penn State University and is a trained NWS SKYWARN Storm Spotter.

Credits

• Sun and Moon data from the U.S. Naval Observatory, with additional astronomical information from timeanddate.com.
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• Through December 2026, additional archived Apex Wx weather data are available through the University of Utah's MesoWest.
• Current and archived Apex Wx weather data are available through Synoptic Data, the successor to MesoWest.
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