The temperatures in Boulder in September are comfortable with low of 10°C and and high up to 21°C.
You can expect about 3 to 8 days of rain in Boulder during the month of September. It’s a good idea to bring along your umbrella so that you don’t get caught in poor weather.
Our weather forecast can give you a great sense of what weather to expect in Boulder in September 2025.
If you’re planning to visit Boulder in the near future, we highly recommend that you review the 14 day weather forecast for Boulder before you arrive.
Temperatures
21° / 10°
Rainy Days
4
Snowy Days
0
Dry Days
25
Rainfall
66
mm
Sun Hours
11.7
Hrs
