Flagstaff Weather in September

The climate in Flagstaff during September can be summarized as mild and reasonably dry.

September is in the fall / autumn in Flagstaff and is typically the 4th warmest month of the year. Daytime maximum temperatures average around a cool 23°C (73°F), whilst at night 3°C (37°F) is normal.

On average September is the 6th wettest month of the year in Flagstaff with around 49mm 1.9 inches of rain making it a reasonably dry time to visit. This rainfall is typically spread over 7 days, although this may vary considerably.

On the flip side this corresponds to an average of 10.6 hours of sunshine per day.

The data used in these monthly averages covers a period of over 100 years right up until last year. As such they are a valid prediction of what to expect for the weather in Flagstaff in September 2025.