The temperatures in Longmont in September are comfortable with low of 13°C and and high up to 28°C.
The wather in Longmont in September can vary between cold and nice weather days. Expect a few rainy days but usually not more than 3.
Our weather forecast can give you a great sense of what weather to expect in Longmont in September 2025.
If you’re planning to visit Longmont in the near future, we highly recommend that you review the 14 day weather forecast for Longmont before you arrive.
Temperatures
28° / 13°
Rainy Days
2
Snowy Days
0
Dry Days
28
Rainfall
35
mm
Sun Hours
11.8
Hrs
