Thornton Weather in September

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

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

September is in the fall / autumn in Thornton and is typically the 4th warmest month of the year. Daytime maximum temperatures average around a comfortable 25°C (77°F), whilst at night 9°C (48°F) is normal.

Thornton weather averages (imperial / metric)
Daytime temperature 24.8°C 76.6°F
Nightly temperature 8.7°C 47.6°F
Average temperature 16.7°C 62.1°F
Daily sunshine 9.8 hrs
Avg rainfall 32 mm 1.2 ins
Rainy days 7 days
Sea temperature 18.3°C 65°F
Humidity 50%
Windspeed 14.8kph 9 mph

On average September is the 6th driest month of the year in Thornton with around 32mm 1.2 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 Thornton

Thornton average temperature in September

September rainfall

Thornton average rain in September

September hourly sunshine

Thornton 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 Thornton 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

Thornton weather stats

Thornton weather statistics
Hottest month: July 30.6°C 87.1°F
Driest month: January 12mm 0.5ins
Sunniest month: September 9.8hrs
Coldest month: January 5.8°C 42.4°F
Wettest month: May 71mm 2.8ins
Map showing location of Thornton (39.86804, -104.97192) Thornton map pin © Google

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