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Tuesday, September 15 – Thursday, September 17

Overview: High pressure building across northern New England is bringing a much quieter weather pattern to the Saint John Valley following Monday’s unsettled conditions. Clear skies, light winds, and dry air allowed temperatures to fall into the 30s early Tuesday morning, producing areas of frost in colder locations and some patchy river-valley fog. Any remaining fog or frost will disappear quickly after sunrise as temperatures recover.

The center of high pressure will gradually move east today, allowing winds to turn southerly. This will begin a period of warmer air moving into northern Maine. Clouds will increase at times today and tonight, but the air remains dry enough that no precipitation is expected. Wednesday will be the warmest day of the period as south to southwest flow strengthens ahead of an approaching cold front. Temperatures should reach the lower 70s across the Saint John Valley, with some afternoon wind gusts around 20 mph.

The approaching front has slowed somewhat and is now expected to reach northern Maine later Thursday or Thursday night. Thursday should therefore remain largely dry, with morning valley fog followed by increasing clouds and temperatures in the mid-60s. A few showers may accompany the front Thursday evening or overnight, but moisture will be limited and rainfall amounts are expected to be small. This system is unlikely to provide meaningful relief from the recent dry conditions.

Overall, the period from Tuesday through Thursday will feature dry and increasingly mild weather through Wednesday, followed by increasing clouds and a slight chance of showers as a weak front approaches Thursday night.

Tuesday: A chilly early-autumn morning gives way to a pleasant and increasingly mild day. Patchy frost and localized Saint John/Fish River valley fog should dissipate early, followed by sunshine this morning and gradually increasing clouds this afternoon. Winds will be light initially, becoming southerly near 5–6 mph as the surface high moves east. Expect a high in the middle 60s. Tonight becomes mostly cloudy for a time as warmer air moves northward, with a south wind around 5–10 mph. Unlike this morning, temperatures should remain quite mild overnight, generally in the low 50s, eliminating the frost concern.

Wednesday: The warmest and probably the most pleasant day of the period. After some morning cloudiness, skies should become mostly sunny as Fort Kent lies within strengthening southwesterly flow ahead of the approaching front. Temperatures rise well above Tuesday’s levels, reaching the low 70s. South to southwest winds of 5–10 mph increase somewhat during the day, with occasional gusts around 20–22 mph, then turn more westerly later. Wednesday evening should remain mostly clear before some clouds return overnight. Winds diminish and patchy valley fog may develop toward morning. Overnight lows fall into the lower to middle 40s.

Thursday: Patchy early-morning fog should lift, leaving a partly sunny start before clouds gradually increase ahead of the approaching frontal boundary. The slower frontal timing now favors keeping most or perhaps all of Thursday daylight hours dry in the Fort Kent area. Temperatures will be cooler than Wednesday but still seasonably mild, with highs in the mid-60s and generally light winds. A few showers become possible Thursday evening or overnight as the weakening front crosses the region, but rainfall should be light and spotty rather than a substantial wetting rain. Patchy fog may redevelop overnight, with lows in the mid to upper 40s.

Friday, September 18 – Monday, September 21

Overview:  Behind the cold front expected to move through Thursday night, cooler and drier air will move into northern Maine Friday as high pressure begins building toward the region. Any lingering clouds or patchy valley fog should give way to increasing sunshine, although a northwest breeze may make the cooler air more noticeable. High pressure will provide mostly clear skies and diminishing winds Friday night, allowing temperatures to fall into the upper 30s to around 40. The normally colder valleys and sheltered locations may again need to be watched for frost.

High pressure should remain in control for much of Saturday, bringing another dry and seasonably cool day. Clouds will begin increasing later Saturday as the high moves east and another disturbance approaches from the west. A weak frontal boundary associated with this system should bring a chance of showers Saturday night into Sunday. At present, moisture again appears limited, favoring scattered showers and periods of dry weather rather than a widespread or prolonged rain. Sunday should consequently be the more unsettled day of the weekend, with considerable cloudiness helping to hold afternoon temperatures around the upper 50s to near 60.

The disturbance should move east Sunday night, with shower chances diminishing as high pressure begins to return. Monday currently favors drier weather with at least partial sunshine and seasonably cool temperatures. With several nights during this period potentially falling into the upper 30s, frost and valley fog will remain features to watch as the forecast becomes more certain.

Friday: Any lingering effects from Thursday night's weak frontal passage should end early, followed by a dry and increasingly sunny day. A northwest breeze may be noticeable during the morning and afternoon as cooler, drier air settles into the Saint John Valley. Temperatures should reach the lower to middle 60s. Skies become mostly clear Friday night as high pressure builds closer to the region. Winds diminish, allowing temperatures to fall into the upper 30s to around 40, with patchy valley fog possible toward morning. Colder sheltered locations may need to be monitored for frost.

Saturday: Saturday should begin mostly sunny and cool under high pressure. Sunshine will likely give way to increasing clouds later in the day as another disturbance approaches from the west. Temperatures will be cooler than Friday, with highs around the lower 60s. Saturday evening should become mostly cloudy, with a chance of showers developing overnight. Rainfall should remain light and scattered based on current guidance. Overnight lows should settle around 40.

Sunday: Sunday looks like the most unsettled day of the period as the disturbance and weak frontal boundary cross northern Maine. Expect considerable cloudiness with a chance of showers, although periods of dry weather are also likely and a prolonged soaking rain does not appear likely. Temperatures should remain on the cool side, with highs around 60. Shower chances diminish Sunday evening and night as the system moves east. Partial clearing may follow, with overnight lows falling into the upper 30s.

Monday: High pressure should begin rebuilding into the region behind Sunday's disturbance. Current indications favor a return to mostly sunny and dry weather, although some clouds may linger depending on the speed of the departing system. Temperatures remain seasonably cool, with highs in the lower 60s. Monday night should remain partly cloudy and chilly, with lows around 40. Patchy valley fog may develop during the cooler nights of the period, while temperatures in the normally colder sheltered locations will bear watching.

Long Range: Tuesday, September 22 – Monday, September 28

CPC favors equal chances for temperature and below-normal precipitation across Fort Kent and the Saint John Valley. High pressure associated with developing ridging over eastern Canada should favor generally quieter and drier conditions across northern Maine. Normal late-September temperatures are daytime highs in the lower to mid-60s and overnight lows in the lower 40s, with averages gradually declining. Equal chances means CPC does not favor a warmer, cooler, or near-normal temperature outcome.

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.
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