Apex Wx

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

Overview: The weak system that brought clouds and scattered showers Sunday has moved east, allowing cooler and drier northwest flow to spread across northern Maine today. Some lingering low clouds or patchy valley fog may persist early before increasing sunshine develops. Northwest winds will become somewhat breezy during the afternoon, with gusts around 20–25 mph, then diminish this evening as Canadian high pressure builds toward the region.

High pressure becomes the dominant weather feature Tuesday and Wednesday, bringing an increasingly quiet stretch of dry weather. Mostly sunny skies and light winds are expected, while the cool air mass gradually moderates. Highs should rise from the mid-50s today to around 60°F Tuesday and into the lower to mid-60s Wednesday.

Clear skies, dry air, and diminishing winds will also favor efficient nighttime cooling. Temperatures should fall into the 30s both Monday and Tuesday nights, with colder sheltered portions of the Saint John Valley potentially approaching freezing. Frost will remain possible, particularly toward Tuesday and Wednesday mornings. No significant precipitation or wind concerns are expected after today.

Monday: Any early patchy fog or low clouds should dissipate, followed by a mainly dry day with increasing sunshine. Highs will reach the mid-50s, with northwest winds around 10 mph and occasional gusts of 20–25 mph. Monday night becomes mostly clear and chilly as winds diminish. Lows should fall into the lower to middle 30s, with patchy frost possible in colder sheltered portions of the Valley.

Tuesday: Canadian high pressure will provide a sunny, dry, and seasonably cool day. After a chilly start with some patchy frost possible, temperatures should recover into the upper 50s to around 60°F, with light northerly winds. Tuesday night will be mostly clear and cold, with lows generally in the lower 30s. Widespread frost is possible after 5 a.m.

Wednesday: High pressure remains firmly in control, providing another sunny and dry day. The air mass begins to moderate, with highs climbing into the lower to mid-60s and winds remaining light. Wednesday night should be clear and chilly, with lows generally in the lower to middle 30s. Patchy valley fog may develop overnight where winds become calm.

Thursday, September 24 – Sunday, September 27

Overview: High pressure and upper-level ridging will remain influential across northern Maine Thursday, continuing the dry weather from midweek while allowing temperatures to moderate. Abundant sunshine and light winds should help afternoon temperatures climb well into the 60s after another chilly start.

The forecast becomes more uncertain Friday into the weekend as an upper-level trough over the eastern United States may evolve into a slow-moving cut-off low. Current guidance agrees on the general development of this system but continues to differ on its eventual position and evolution. Those differences will determine how far north its clouds and precipitation extend.

For now, the Saint John Valley appears likely to remain north of the system’s primary influence, with current NWS guidance favoring mainly dry conditions through Sunday. Friday could be the warmest day if sunshine remains plentiful, with temperatures reaching the upper 60s and potentially somewhat higher. Some additional cloud cover is possible Saturday and Sunday, but significant rainfall is not presently indicated. The position and evolution of the slow-moving low remain the principal forecast uncertainties for the weekend.

Thursday: High pressure will provide another sunny and dry day, with temperatures continuing to moderate. Highs should reach the mid- to upper 60s, with light winds. Thursday night will be partly cloudy and not as cold as earlier in the week, with lows around the upper 30s to lower 40s.

Friday: Mostly sunny to partly cloudy skies are expected as the Saint John Valley remains north of the primary influence of the developing eastern system. Temperatures should reach the upper 60s, although some guidance is several degrees warmer. Current NWS guidance maintains only a minimal chance of precipitation across northern Maine. Friday night should be partly to mostly cloudy, with lows in the lower to mid-40s.

Saturday: Current guidance favors a mainly dry day across the Valley, with a mix of sun and clouds and highs in the mid- to upper 60s. A slight chance of a shower or two cannot be completely ruled out if moisture reaches farther north than currently expected. Saturday night should remain partly to mostly cloudy with lows in the lower 40s.

Sunday: The Valley should remain largely removed from the more unsettled weather farther south. Partly to mostly sunny skies and mainly dry conditions are favored, with highs generally in the mid-60s. Sunday night will be partly cloudy, with temperatures falling into the lower 40s.

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.

Weather Apps

Most weather apps rely heavily on automated forecast data. They can be useful for a quick look at routine weather, but automated forecasts may miss important local details or the significance of rapidly changing conditions. During hazardous or changing weather, consult weather.gov and other official National Weather Service information rather than relying solely on an app.

Radar Apps

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.