Flagstaff weather in September
September in Flagstaff: nice, dry, with clean air — one of the best months to visit.
Updated September 2026 · climate normals from ERA5 reanalysis
#1 of 12 months in Flagstaff · #42 of 1413 destinations to visit in September · comfort 94/100 (tier S)
- Days
- 24°C
- Nights
- 9°C
- Wet days
- 5
- Sun
- 11.1 h
- Humidity
- 49%
- Daylight
- 12 h
Traveller notes on Flagstaff in September
Late September into early October is the window regulars name for this part of Arizona: temperatures cooling, patterns fairly stable and mostly sunny, crowds thinning. Flagstaff sits at about 7,000 feet, which is the whole point — days near 25°C while the desert below is still hot, and nights dropping to about 13, cold enough that a jacket or fleece is wanted early and late, with freezing possible in the second half of the month. The third week of September is when aspen, oak and birch begin turning on the Grand Canyon's North Rim. Layers you can shed is the standing advice.
Other months in Flagstaff
Forum posters cite an average March daytime high around 43F with nighttime lows in the teens, describing March as still genuinely winter in Flagstaff - posters are direct that snow at some point during the month is close to guaranteed, unless an unusually warm stretch arrives early. Posters describe a typical late-winter snowfall here as brief, usually gone within a day or two, with roads cleared quickly except during a major storm, which can shut down travel for several days at a time. Posters consistently recommend monitoring forecasts roughly a week ahead and building real flexibility into a March itinerary. Posters generally rate March as a high-precipitation, snow-capable month, workable for a visit but requiring genuine weather-contingency planning.
Add your own note from Flagstaff's card on the map.
Flagstaff climate normals — September
Monthly averages from ERA5 reanalysis. AQI is the mean US Air Quality Index for the month.
Crowds in Flagstaff in September
How busy the place itself is — school and mass holidays, the months an editor tagged, and how sought-after the weather makes them. Never part of the comfort score.
Peak crowdsAspen colour on the Peaks, Summer break in United States(estimated)
Peak crowdsBusyShoulder seasonQuiet
Best months for Flagstaff's weather
Ranked by this destination's own climate comfort score across the year — a different thing from how busy it gets (see Crowds above).
Best weatherFlagstaff's best weather comes in June, August and September — separate windows, not one continuous season.
September includes Aspen colour on the Peaks.
Best weatherFair weatherToughest weather
What's on in Flagstaff in September
Recurring seasonal events, natural spectacles, closures and holidays — curated and sourced.
- Season
Southwest monsoon
15 Jun – 30 SepRiskStorms build over the Peaks most afternoons from early July, drop hard for an hour and clear, and the burn scars above town flood downhill when they do. It is the greenest and the most dramatic the high desert gets. Source ↗
- Nature
Aspen colour on the Peaks
20 Sep – 15 Oct · usuallyAutumn colourCrowdedThe stands in the Inner Basin and along Hart Prairie turn gold for about a fortnight, starting high and working down. The Lockett Meadow road is single track and the car park is full by nine on an October weekend. Source ↗
- Festival
Flagstaff Festival of Science
25 Sep – 4 OctMajor festivalTen days of free talks, observatory openings and field trips run by a town that has an astronomy observatory, a university and the US Geological Survey in it. Everything is free and most of it books out. Source ↗
Nearby, and something's on
Within 300 km of Flagstaff — a day trip or a short hop — with something on this month. Never part of the comfort score.
Where is Flagstaff?
Flagstaff in September — FAQ
- Is September a good time to visit Flagstaff?
- September in Flagstaff: nice, dry, with clean air — one of the best months to visit. It ranks #1 of 12 months for Flagstaff on SeasonMap's comfort score (94/100).
- What is the weather like in Flagstaff in September?
- In September, Flagstaff averages a daily high of 24.1°C and a low of 9°C, with about 29.8 mm of rain over roughly 4.5 rainy days.
- What is the air quality in Flagstaff in September?
- Flagstaff has a mean US Air Quality Index of about 41 in September.
Within 300 km: Sedona's Dark-sky season around 15 Sep – 20 Nov, and Zion National Park's California condors over the canyon on 1 Jan – 31 Dec.