Apex Wx

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Saturday, September 19 – Monday, September 21

Overview: A cool, dry Canadian air mass will provide sunny and pleasant early-autumn weather Saturday, although northwest winds will remain somewhat brisk. Winds diminish tonight, and temperatures will fall well into the 30s. Patchy frost is possible in colder locations, but increasing clouds may limit its development.

Clouds become widespread Sunday ahead of an approaching low pressure area and cold front. Most of Sunday morning and early afternoon should remain dry, with the chance of showers increasing later in the afternoon and becoming greatest Sunday evening and early Sunday night. Rainfall should be light and spotty rather than a widespread soaking rain.

The front moves through by Monday, with any lingering shower threat largely confined to the morning. Drier air and some sunshine should return during the day as high pressure builds in from Canada. Clearing skies Monday night will bring another chilly night, with temperatures falling into the 30s and patchy frost possible in colder portions of the Saint John Valley.

Saturday: A crisp and predominantly sunny September day. After the chilly morning, temperatures recover only slowly under continued cool northwest flow, with an afternoon high in the middle 50s. Northwest winds around 10 mph, occasionally gusting to around 20 mph during the afternoon, will add to the cool feel despite abundant sunshine. Skies remain mostly clear this evening before some clouds begin increasing later tonight. Winds become light, allowing temperatures to fall into the middle 30s around Fort Kent, with lower 30s possible in colder sheltered locations. Patchy frost is possible, especially away from area rivers and lakes.

Sunday: Clouds will increase during the morning, leading to a mostly cloudy to cloudy day, but most of the morning and early afternoon should remain dry. A slight chance of a shower develops by mid-afternoon, with the chance increasing during the late afternoon and evening. Highs will reach the middle 50s, with light southerly winds. Scattered showers remain possible Sunday evening and into the first part of the night before gradually becoming less numerous toward morning. Patchy fog may develop overnight. Lows will fall into the middle 30s.

Monday: A lingering shower will remain possible early Monday morning as the cold front moves east, but most of the day should be dry. Clouds will gradually break for some sunshine as drier air arrives behind the front. Temperatures will remain cool, with highs in the middle 50s, while northwest winds become breezy with gusts 20-25 mph during the afternoon. Skies should continue clearing Monday evening and night as Canadian high pressure builds into the region. Lows will fall into the lower to middle 30s, with patchy frost possible, particularly in sheltered valleys and colder locations.

Tuesday, September 22 – Friday, September 25

Overview: Weak high pressure should remain influential after Monday, bringing a quiet and mostly dry stretch to northern Maine Tuesday through Thursday. Sunshine and light winds will allow temperatures to gradually moderate, with highs rising from the lower 60s Tuesday into the mid-60s Wednesday and Thursday. Nights will remain cool, generally in the lower 40s, but the frost concern should be less pronounced than during the preceding period. Current NWS guidance keeps precipitation chances very low through Wednesday.

The pattern becomes somewhat less certain late Thursday into Friday as high pressure shifts east and a disturbance tracks across southern New England. Clouds may increase across northern Maine, but current NWS guidance keeps the Saint John Valley dry through Friday. The main forecast question is how far north the system’s moisture and precipitation will extend, with current model guidance offering differing solutions. Temperatures should remain relatively mild, with highs reaching the mid-60s.

Tuesday: High pressure will provide a sunny, dry, and seasonably cool day, with highs in the upper 50s and light winds. Tuesday night will be clear and chilly, with temperatures falling into the lower 30s. Frost is likely to become a greater concern, particularly in colder and sheltered portions of the Valley.

Wednesday: The quiet pattern continues as high pressure remains in control and the cool air mass begins to moderate. Sunny skies are expected, with highs in the lower 60s. Wednesday night will remain clear, with lows again falling into the lower 30s, maintaining the potential for frost.

Thursday: High pressure should remain influential, although some increase in cloud cover is possible later in the day as a disturbance tracks toward southern New England. Skies should range from mostly sunny to partly sunny, with highs in the mid-60s. Thursday night will be partly cloudy with lows in the upper 30s. Current NWS guidance keeps most precipitation south of the Valley.

Friday: The southern New England disturbance may bring somewhat more cloud cover to northern Maine, but its northern extent remains uncertain. Current NWS guidance continues to favor dry conditions, with partly sunny to mostly sunny skies and highs in the mid-60s. Friday night should be partly cloudy and cool, with lows in the upper 30s.

Long Range: Saturday, September 26 – Friday, October 2

The latest outlook favors above-normal temperatures and below-normal precipitation across the Saint John Valley. Broad ridging across central and eastern Canada supports the warmer tendency, while the expected circulation favors a generally drier pattern across northern Maine. Normal temperatures during the period are generally in the upper 50s for daytime highs and upper 30s overnight.

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.
• NOAA warning banner provided by WillyWeather.com.
• 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.
• Apex Wx logo by Joanna Becker © 2016. Visit Bushi and Brush Arts Dojo.

How accurate are forecasts?

Forecast confidence generally decreases as lead time increases. Forecasts for the next few days usually provide considerably more detail and confidence than forecasts a week or more in advance. Beyond about 7 days, forecasts are most useful for identifying broader weather patterns and temperature or precipitation trends rather than predicting exact conditions at a particular place and time.

Individual computer-model runs—especially those depicting specific storms, snowfall amounts, or other details a week or more in advance—should not be treated as forecasts by themselves. Extended forecasts will change as new observations become available and models better resolve the evolving atmospheric pattern. Check updated forecasts as the event approaches.

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Weather radar is an invaluable tool for tracking precipitation and storms, but radar images should not be interpreted as a real-time picture of conditions at the ground. Data collection, processing, transmission, mosaicking, and app updates can introduce delays, and radar detects energy returned from precipitation at varying heights above the surface. During rapidly developing or moving storms, conditions at your location may therefore differ from what a radar app appears to show. Use radar together with current observations and official National Weather Service warnings.