Apex Wx

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Friday, September 18 – Sunday, September 20

Overview: A cold front and upper-level trough crossing northern Maine today will usher in a much cooler and drier Canadian air mass. A few light showers are possible early, but the main weather concern will be strengthening northwest winds. Daytime mixing will allow gusts to reach 30–35 mph, with isolated downed limbs or power interruptions possible while trees remain substantially leafed.

High pressure builds toward northern New England tonight and Saturday, allowing winds to diminish and bringing a sunny, dry, and cool start to the weekend. Light winds and clearing Saturday night will favor strong cooling, with localized frost possible in sheltered areas as temperatures fall into the mid-30s.

The high shifts east Sunday as a weak cold front approaches. Clouds will increase, but moisture remains limited and current guidance favors a mostly dry day in the Valley, with only isolated light showers possible late Sunday afternoon and evening.

Friday: A few light showers are possible early this morning as the front and upper trough cross northern Maine, but most of the day will be dry with increasing sunshine. Temperatures will reach only the upper 50s to around 60°F. The main concern will be strengthening northwest winds, increasing to 15–20 mph during the afternoon with gusts around 30–35 mph. Friday night will be mostly clear and chilly. Northwest winds remain somewhat gusty during the evening before diminishing, with lows falling into the mid-30s. Some patchy frost may be possible after midnight.

Saturday: High pressure will provide a sunny, dry, and cool day. Highs should remain in the mid- to upper 50s, several degrees below normal. Northwest winds around 5–10 mph may occasionally gust near 20 mph, but conditions will be substantially calmer than Friday. Saturday night will be partly cloudy to mostly clear with winds becoming calm. Temperatures fall into the mid-30s, creating the possibility of localized frost in colder sheltered areas.

Sunday: After a chilly start, clouds will gradually increase as high pressure moves east and a weak disturbance approaches. Current guidance favors a mostly dry day, with only a 20% chance of showers developing after about 3 PM. Highs should recover into the upper 50s to around 60°F, with light south winds around 5 mph. A slight chance of showers continues during the evening before ending, with mostly cloudy skies Sunday night and lows in the upper 30s.

Monday, September 21 – Thursday, September 24

Overview: Weak high pressure returning behind Sunday’s cold front should bring a quieter start to the new week. Monday will be mainly dry and seasonably cool, followed by another chilly night as partial clearing and light winds allow temperatures to fall into the mid-30s in most locations. Sheltered portions of the Valley may again approach temperatures favorable for localized frost.

High pressure becomes more firmly established Tuesday and remains influential through Thursday, producing an extended stretch of dry weather. Mostly sunny skies and light winds are expected, while the cool air mass gradually moderates. Daytime temperatures should rise from around 60°F Monday into the lower 60s Tuesday and mid-60s Wednesday and Thursday. Nights remain cool, particularly early in the period, but the overall trend is toward somewhat milder conditions by midweek. No significant precipitation, wind, or thunderstorm concerns are evident through Thursday.

Monday: Any early patchy valley fog should dissipate after sunrise, followed by a mainly dry day with a mix of sun and clouds. Temperatures should reach the upper 50s to around 60°F, with light winds. Monday night will be partly cloudy and chilly, with lows in the mid-30s. Localized frost may develop in colder sheltered areas where skies clear and winds become calm.

Tuesday: High pressure becomes more firmly established, providing a dry day with mostly sunny skies. Highs should reach the lower 60s, with light winds. Tuesday night will be mostly clear and chilly, with lows falling into the lower 30s, so the potential for a more widespread frost will need to be monitored.

Wednesday: The quiet pattern continues, but temperatures begin to moderate as the cool air mass modifies beneath developing ridging. Sunny skies are expected, with highs climbing into the mid-60s. Wednesday night should remain mostly clear to partly cloudy, with lows generally in the middle 30s.

Thursday: High pressure should remain influential through the day, maintaining dry and mostly sunny weather. Temperatures continue their gradual rebound, with highs in the mid-60s. Clouds begin increasing Thursday night as the next disturbance approaches, with a 20% chance of showers after 2 AM. Lows will fall into the lower 40s.

Long Range: Friday, September 25 – Thursday, October 1

CPC guidance places the Saint John Valley within equal chances for both temperature and precipitation during the period, meaning there is not strong signal for above or below normal conditions at present. Broad ridging remains prominent across central North America, while increased troughing near the East Coast introduces greater uncertainty across the Northeast. Normal temperatures for the Valley during this late-September period are generally in the upper 50s to around 60°F for daytime highs, with overnight lows in the upper 30s to around 40°F.

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.

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