Longmont Weather in September

What's the weather like in Longmont (Colorado) in September 2025?

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

September is in the fall / autumn in Longmont and is typically the 4th warmest month of the year. Daytime maximum temperatures average around a comfortable 24°C (75°F), whilst at night 8°C (47°F) is normal.

Longmont weather averages (imperial / metric)
Daytime temperature 24.1°C 75.3°F
Nightly temperature 8.2°C 46.7°F
Average temperature 16.1°C 61°F
Daily sunshine 9.8 hrs
Avg rainfall 35 mm 1.4 ins
Rainy days 7 days
Sea temperature 17.6°C 63.7°F
Humidity 50%
Windspeed 15.1kph 9 mph

On average September is the 6th wettest month of the year in Longmont with around 35mm 1.4 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 9.8 hours of sunshine per day.

September temperatures in Longmont

Longmont average temperature in September

September rainfall

Longmont average rain in September

September hourly sunshine

Longmont average rain in September

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 Longmont in September 2025.

Other monthly averages

Best places to visit in September

UV index Best time to go?

Beta

Current (hourly) weather 15 day forecast

Longmont weather stats

Longmont weather statistics
Hottest month: July 29.9°C 85.8°F
Driest month: January 13mm 0.5ins
Sunniest month: September 9.8hrs
Coldest month: January 5.2°C 41.4°F
Wettest month: May 74mm 2.9ins
Map showing location of Longmont (40.16721, -105.10193) Longmont map pin © Google

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