Boulder County (Boulder)
September
Weather in Boulder County, Colorado for September 2026
Your guide to Boulder County weather in September - trends and predictions
So far, September 2026 in Boulder County is slightly warmer than the historical average by 1.4 °F.
The forecast for the next days in Boulder County predicts temperatures to be around 22 °F, close to the historical average.
In general, the average temperature in Boulder County 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 County 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 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° /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 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 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 County during September?
Moderate rainfall is anticipated in Boulder County 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 County during September?
The average wind speed in Boulder County during September is 18 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 💧
Typically, Boulder County has 13 rainy days in September with a total of 60.6 mm of rainfall.
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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