Boulder (CO)
September
Weather in Boulder, Colorado for September 2026
Your guide to Boulder weather in September - trends and predictions
So far, September 2026 in Boulder is slightly warmer than the historical average by 1.4 °F.
The forecast for the next days in Boulder predicts temperatures to be around 22 °F, close to the historical average.
In general, the average temperature in Boulder at the beginning of September is 27.1 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 22.4 °F by the end of September.
The climate of Boulder in September is notably wet, with an average of 13 rainy days, and a total of 60.6 mm of precipitation.
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Temperatures
Rain 🌧️
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17
Dry days
13
Rainy days
0
Snow days
25°/12°
Temperatures
18 km/h
Avg max wind
41 %
Avg humidity
Boulder Weather September
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Temperatures trend during September in Boulder
See the weather trend as well as the moving average line
September weather in Boulder day by day
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| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 |  Sunny | 27° /14° | 0.1 mm | 6 | |
| Sept. 2 | Sunny | 27° /14° | 0.1 mm | 8 | |
| Sept. 3 |  Cloudy | 29° /14° | 0 mm | 7 | |
| Sept. 4 | Sunny | 30° /14° | 3 mm | 8 | |
| Sept. 5 |  Patchy rain possible | 24° /12° | 0.8 mm | 6 | |
| Sept. 6 | Sunny | 25° /11° | 1 mm | 6 | |
| Sept. 7 | Cloudy | 28° /14° | 0.6 mm | 5 | |
| Sept. 8 |  Partly cloudy | 28° /15° | 0.3 mm | 6 | |
| Sept. 9 | Cloudy | 27° /14° | 0 mm | 7 | |
| Sept. 10 |  Overcast | 28° /12° | 4.1 mm | 7 | |
| Sept. 11 |  Moderate or heavy rain shower | 27° /14° | 4.6 mm | 5 | |
| Sept. 12 | Partly cloudy | 26° /12° | 1.6 mm | 6 | |
| Sept. 13 | Partly cloudy | 26° /11° | 2.7 mm | 6 | |
| Sept. 14 | Sunny | 27° /12° | 1 mm | 5 | |
| Sept. 15 | Cloudy | 26° /11° | 0.1 mm | 7 | |
| Sept. 16 | Overcast | 25° /11° | 3.8 mm | 4 | |
| Sept. 17 | Overcast | 23° /12° | 0.9 mm | 4 | |
| Sept. 18 | Sunny | 23° /9° | 0.9 mm | 4 | |
| Sept. 19 | Partly cloudy | 25° /10° | 0.8 mm | 6 | |
| Sept. 20 | Cloudy | 25° /11° | 0.4 mm | 6 | |
| Sept. 21 | Cloudy | 22° /9° | 5.2 mm | 6 | |
| Sept. 22 | Patchy rain possible | 20° /9° | 11.1 mm | 4 | |
| Sept. 23 | Cloudy | 20° /8° | 1.8 mm | 3 | |
| Sept. 24 | Partly cloudy | 20° /9° | 0.8 mm | 4 | |
| Sept. 25 | Sunny | 25° /9° | 0.4 mm | 5 | |
| Sept. 26 | Sunny | 27° /12° | 0 mm | 6.5 | |
| Sept. 27 | Overcast | 26° /14° | 0.2 mm | 6.2 | |
| Sept. 28 | Overcast | 21° /13° | 4.9 mm | 4.9 | |
| Sept. 29 | Overcast | 17° /12° | 0.2 mm | 3.4 | |
| Sept. 30 | Overcast | 21° /12° | 0.3 mm | 6.6 | |
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Important Notice
Our weather forecast for Boulder 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 forecast closer to your planned date for the most up-to-date weather information.
Change Month
Boulder in September - FAQ
What are the expected maximum and minimum temperatures in Boulder during September?
Enjoy moderate daytime temperatures of up to 25° 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 during September?
Moderate rainfall is anticipated in Boulder during September, with a total of 60.6 mm spread over approximately 13 days. Considering plans for rainy days is advisable.
What are the typical wind conditions in Boulder during September?
The average wind speed in Boulder during September is 18 km/h, suggesting breezy to windy conditions, depending on your activities.
September rainfall patterns in Boulder
Explore the daily rainfall trends and prepare for Boulders September weather 💧
Typically, Boulder has 13 rainy days in September with a total of 60.6 mm of rainfall.
UV exposure in Boulder during September
Stay informed about UV levels for safe outdoor activities throughout the month of September ☀️
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