September in Flagstaff averages a daily high of 23.4°C with nights around 6.1°C. Expect roughly 7.7 wet days totalling 44.7mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Flagstaff is May–June.
Based on FLAGSTAFF AIRPORT, AZ US (6.1km), 1995–2024. 30 years of September data.