Helena Weather in September

The climate in Helena during September can be summarized as hot, humid and a little damp.

September is in the fall / autumn in Helena and is typically the 4th warmest month of the year. Daytime maximum temperatures average around a muggy 29°C (85°F), whilst at night 17°C (63°F) is normal.

On average September is the 3rd driest month of the year in Helena with around 85mm 3.4 inches of rain making it a a little damp time to visit. This rainfall is typically spread over 8 days, although this may vary considerably.

On the flip side this corresponds to an average of 9 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 Helena in September 2025.