Boulder County (Boulder)
September
Weather in Boulder County for September 2025
Your guide to Boulder County weather in September - trends and predictions
In general, the average temperature in Boulder County at the beginning of September is 26.3 °F. As the month progressed, temperatures tended to moderately rise, reaching an average of 27.9 °F by the end of September.
With an average of 5 rainy days, Boulder County experiences minimal rainfall in September.
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Temperatures
Rain 🌧️
More
25
Dry days
5
Rainy days
0
Snow days
26°/12°
Temperatures
17 km/h
Avg max wind
36 %
Avg humidity
Boulder County Weather September
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| Sun. | Mon. | Tue. | Wed. | Thu. | Fri. | Sat. |
|---|---|---|---|---|---|---|
| 1  28° | 2  28° | 3 30° | 4  26° | 5  21° | 6 25° | |
| 7 26° | 8  28° | 9 28° | 10  27° | 11 25° | 12 29° | 13 23° |
| 14 27° | 15 27° | 16 26° | 17 27° | 18 25° | 19 25° | 20 27° |
| 21  17° | 22 12° | 23 23° | 24 21° | 25 28° | 26 31° | 27 28° |
| 28 29° | 29 30° | 30 28° |
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Temperatures trend during September in Boulder County
See the weather trend as well as the moving average line
September weather day by day
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| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 | Sunny | 28° /14° | 0 mm | 7 | |
| Sept. 2 | Cloudy | 28° /14° | 0 mm | 6 | |
| Sept. 3 | Cloudy | 30° /15° | 0 mm | 7 | |
| Sept. 4 | Moderate or heavy rain shower | 26° /14° | 9.1 mm | 6 | |
| Sept. 5 | Patchy rain possible | 21° /13° | 2.3 mm | 5 | |
| Sept. 6 | Sunny | 25° /11° | 0 mm | 7 | |
| Sept. 7 | Cloudy | 26° /13° | 0 mm | 6 | |
| Sept. 8 | Partly cloudy | 28° /14° | 0 mm | 7 | |
| Sept. 9 | Cloudy | 28° /16° | 0 mm | 6 | |
| Sept. 10 | Overcast | 27° /16° | 0 mm | 6 | |
| Sept. 11 | Moderate or heavy rain shower | 25° /14° | 3.3 mm | 6 | |
| Sept. 12 | Partly cloudy | 29° /12° | 0 mm | 7 | |
| Sept. 13 | Partly cloudy | 23° /11° | 0 mm | 6 | |
| Sept. 14 | Sunny | 27° /12° | 0 mm | 7 | |
| Sept. 15 | Cloudy | 27° /13° | 0 mm | 6 | |
| Sept. 16 | Overcast | 26° /13° | 0 mm | 6 | |
| Sept. 17 | Overcast | 27° /12° | 0 mm | 6 | |
| Sept. 18 | Sunny | 25° /8° | 0 mm | 7 | |
| Sept. 19 | Partly cloudy | 25° /11° | 0 mm | 7 | |
| Sept. 20 | Cloudy | 27° /13° | 0 mm | 6 | |
| Sept. 21 | Heavy rain at times | 17° /10° | 15.3 mm | 4 | |
| Sept. 22 | Moderate or heavy rain shower | 12° /6° | 31.1 mm | 3 | |
| Sept. 23 | Cloudy | 23° /7° | 0 mm | 5 | |
| Sept. 24 | Partly cloudy | 21° /10° | 0 mm | 6 | |
| Sept. 25 | Sunny | 28° /11° | 0 mm | 7 | |
| Sept. 26 | Sunny | 31° /14° | 0 mm | 8 | |
| Sept. 27 | Cloudy | 28° /16° | 0 mm | 6 | |
| Sept. 28 | Sunny | 29° /14° | 0 mm | 7 | |
| Sept. 29 | Sunny | 30° /14° | 0 mm | 8 | |
| Sept. 30 | Cloudy | 28° /12° | 0 mm | 6 | |
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Important Notice
Our weather forecast for Boulder County in September is based on the analysis of historical data rather than real-time forecast models. While this provides a general overview, weather conditions can change. We recommend that you check the Boulder County forecast closer to your planned date for the most up-to-date weather information.
Boulder County in September - FAQ
What are the expected maximum and minimum temperatures in Boulder County during September?
Enjoy moderate daytime temperatures of up to 26° and cooler nights around 12°. Ideal for a range of outdoor activities, from hiking to city tours.
How much rainfall should be expected in Boulder County during September?
Moderate rainfall is anticipated in Boulder County during September, with a total of 61.2 mm spread over approximately 5 days. Considering plans for rainy days is advisable.
What are the typical wind conditions in Boulder County during September?
The average wind speed in Boulder County during September is 17 km/h, suggesting breezy to windy conditions, depending on your activities.
September rainfall patterns in Boulder County
Explore the daily rainfall trends and prepare for Boulder Countys September weather 💧
UV exposure in Boulder County during September
Stay informed about UV levels for safe outdoor activities throughout the month of September ☀️
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