Apex Wx

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Tuesday, September 22 – Thursday, September 24

🍂 The Autumnal Equinox occurs Tuesday, September 22 at 8:05 p.m. EDT 🍂

Overview: Canadian high pressure centered across Quebec and northern New England will dominate the weather through Thursday, providing an extended stretch of dry and mostly sunny conditions. The air mass remains cool initially, but gradual moderation will occur as weak upper-level ridging develops. Daytime temperatures should rise from around 60°F today into the lower to mid-60s Wednesday and mid- to upper 60s Thursday, with light north to northeast winds.

The main local concern will be nighttime cooling. Clear skies, dry air, and light winds will allow temperatures to fall rapidly after sunset, particularly in sheltered portions of the Saint John Valley. Lows should reach the lower 30s tonight and again Wednesday night, with colder locations potentially reaching freezing or slightly below. Frost is likely in colder areas, and localized valley fog may also develop.

Attention turns toward developing low pressure near the Mid-Atlantic coast later in the week. Its eventual track remains uncertain, but current guidance keeps the Saint John Valley dry through Thursday, with any significant precipitation remaining farther south.

Tuesday: After a cold start with frost in some locations, sunny and dry weather will prevail. Temperatures should recover into the upper 50s to around 60°F, with north to northwest winds around 5–10 mph. Tonight will be mostly clear and cold, with lows generally in the lower 30s and colder sheltered locations potentially reaching freezing or slightly below. Patchy to areas of frost are expected, with localized valley fog possible.

Wednesday: Any early frost or patchy valley fog will dissipate after sunrise, followed by another sunny and dry day. Temperatures moderate into the lower to mid-60s, with light north to northeast winds. Wednesday night will again feature excellent radiational cooling conditions. Lows should fall into the middle 30s, with frost developing in colder low-lying and sheltered portions of the Valley.

Thursday: High pressure remains firmly in control, bringing another sunny and dry day. The warming trend becomes more noticeable, with highs reaching the mid- to upper 60s and locally approaching 70°F if sunshine remains uninterrupted. Winds remain light from the north to northeast. Thursday night should be mostly clear to partly cloudy and milder than the preceding nights, with lows in the lower 40s.

Friday, September 25 – Monday, September 28

Overview: Following the dry and increasingly mild weather through Thursday, the pattern becomes more complicated Friday into the weekend as low pressure develops near the Mid-Atlantic coast and becomes separated from the main upper-level flow. Meanwhile, high pressure remains established across Quebec and eastern Canada, maintaining generally dry north to northeast flow across northern Maine.

The cut-off low off the Mid-Atlantic coast will bear watching through the weekend, with guidance continuing to differ on its exact position and northern precipitation extent. Some solutions bring rain into southern or central Maine, while others keep most precipitation offshore. At present, however, guidance consistently keeps significant precipitation south of the Saint John Valley and northern Aroostook County.

As a result, mainly dry weather remains favored locally Friday through Sunday, although periods of increased cloud cover are possible depending on the low’s position. Friday should be the warmest day, with temperatures near 70°F before gradually easing during the weekend. The coastal system should exert less influence by Monday, with seasonably mild and predominantly dry conditions continuing across the Valley.

Friday: Fort Kent and the Valley should remain north of the coastal system’s primary influence. Mostly sunny to partly cloudy skies are expected, with highs in the upper 60s to around 70°F and light north to northeast winds. Clouds may increase somewhat Friday night, but current northern Maine guidance favors dry conditions. Lows should settle into the lower 40s.

Saturday: The position of the coastal low remains important, but current guidance continues to favor mainly dry weather across northern Maine. Expect a mix of sun and clouds with highs in the mid- to upper 60s. North to northeast winds may become somewhat more noticeable as the pressure difference between the coastal low and Canadian high increases. Saturday night should be partly to mostly cloudy with lows in the lower 40s.

Sunday: The Saint John Valley should remain largely removed from the more unsettled conditions farther south. Partly to mostly sunny skies and predominantly dry weather are favored, with highs in the mid- to upper 60s. Some uncertainty remains because of the slow-moving nature of the coastal system, but significant rainfall is not expected currently. Sunday night should be partly cloudy with lows around the lower 40s.

Monday: The coastal system should exert progressively less influence as the new week begins. Partly sunny and mainly dry conditions are favored, with highs generally in the mid-60s. Monday night will be partly cloudy and seasonably cool, with lows in the lower 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.
• 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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