Boulder County (Boulder)
September
Weather in Boulder County, Colorado for September 2025
Your guide to Boulder County weather in September - trends and predictions
Until now, September 2025 in Boulder County is slightly cooler than the historical average by -1.2 °F.
Expect cooler weather in the next days in Boulder County with the forecast suggesting a temperature of 22.6 °F, lower than the historical average.
In general, the average temperature in Boulder County at the beginning of September is 25.9 °F. As the month progressed, temperatures tended to noticeably cool down, reaching an average of 23.7 °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
35 %
Avg humidity
Boulder County Weather September
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Temperatures trend during September in Boulder County
See the weather trend as well as the moving average line
September weather in Boulder County day by day
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| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 |  Sunny | 27° /13° | 0 mm | 7 | |
| Sept. 2 |  Cloudy | 27° /13° | 0 mm | 7 | |
| Sept. 3 | Cloudy | 28° /14° | 0 mm | 7 | |
| Sept. 4 |  Moderate or heavy rain shower | 29° /14° | 4.6 mm | 7 | |
| Sept. 5 |  Patchy rain possible | 20° /10° | 1.1 mm | 5 | |
| Sept. 6 | Sunny | 23° /9° | 0 mm | 7 | |
| Sept. 7 | Cloudy | 27° /13° | 0 mm | 7 | |
| Sept. 8 |  Partly cloudy | 28° /15° | 0 mm | 7 | |
| Sept. 9 | Cloudy | 27° /15° | 0 mm | 6 | |
| Sept. 10 |  Overcast | 27° /14° | 6.1 mm | 6 | |
| Sept. 11 | Moderate or heavy rain shower | 25° /14° | 7 mm | 6 | |
| Sept. 12 | Partly cloudy | 26° /13° | 2.3 mm | 6 | |
| Sept. 13 | Partly cloudy | 23° /11° | 4 mm | 6 | |
| Sept. 14 | Sunny | 25° /9° | 1.5 mm | 6 | |
| Sept. 15 | Cloudy | 27° /13° | 0 mm | 7 | |
| Sept. 16 | Patchy rain possible | 23° /11° | 2.2 mm | 1.3 | |
| Sept. 17 |  Thundery outbreaks possible | 19° /9° | 0 mm | 1.5 | |
| Sept. 18 |  Moderate rain | 20° /8° | 5.5 mm | 1.5 | |
| Sept. 19 | Sunny | 24° /7° | 0 mm | 1.8 | |
| Sept. 20 | Sunny | 25° /15° | 0.1 mm | 0 | |
| Sept. 21 | Sunny | 20° /14° | 0 mm | 5 | |
| Sept. 22 | Sunny | 24° /12° | 0 mm | 5 | |
| Sept. 23 | Sunny | 23° /11° | 0 mm | 5 | |
| Sept. 24 | Patchy rain possible | 26° /13° | 0.1 mm | 4 | |
| Sept. 25 | Sunny | 24° /14° | 0 mm | 5 | |
| Sept. 26 | Sunny | 26° /14° | 0 mm | 5 | |
| Sept. 27 | Patchy rain possible | 23° /12° | 0.1 mm | 4 | |
| Sept. 28 | Sunny | 22° /9° | 0 mm | 4 | |
| Sept. 29 | Sunny | 17° /6° | 0 mm | 4 | |
| Sept. 30 | Cloudy | 28° /12° | 0 mm | 6 | |
| Next | |||||
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.
Change Month
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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