Ada County (Boise)
September
Weather in Ada County, Idaho for September 2026
Your guide to Ada County weather in September - trends and predictions
Until now, September 2026 in Ada County is slightly cooler than the historical average by 1.4 °F.
The forecast for the upcoming days in Ada County predicts a temperature of 26 °F, which is slightly above the historical average.
In general, the average temperature in Ada County at the beginning of September is 29.4 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 24.7 °F by the end of September.
With an average of 5 rainy days, Ada County experiences minimal rainfall in September.
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Temperatures
Rain 🌧️
More
25
Dry days
5
Rainy days
0
Snow days
27°/14°
Temperatures
16 km/h
Avg max wind
37 %
Avg humidity
Ada County Weather September
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Temperatures trend during September in Ada County
See the weather trend as well as the moving average line
September weather in Ada County day by day
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| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 |  Sunny | 34° /18° | 0 mm | 7 | |
| Sept. 2 |  Patchy rain possible | 31° /18° | 0.4 mm | 7 | |
| Sept. 3 | Patchy rain possible | 27° /16° | 9.5 mm | 5 | |
| Sept. 4 | Sunny | 26° /14° | 9.9 mm | 5 | |
| Sept. 5 | Sunny | 30° /15° | 0 mm | 8 | |
| Sept. 6 |  Overcast | 30° /15° | 0.3 mm | 6 | |
| Sept. 7 |  Partly cloudy | 28° /15° | 4.6 mm | 7 | |
| Sept. 8 | Patchy rain possible | 30° /15° | 0.4 mm | 7 | |
| Sept. 9 | Sunny | 28° /14° | 0 mm | 6 | |
| Sept. 10 | Overcast | 28° /15° | 1.7 mm | 6 | |
| Sept. 11 |  Patchy light rain with thunder | 25° /13° | 0.7 mm | 6 | |
| Sept. 12 | Overcast | 23° /12° | 1 mm | 4 | |
| Sept. 13 | Sunny | 23° /13° | 0 mm | 6 | |
| Sept. 14 |  Cloudy | 23° /13° | 0 mm | 6 | |
| Sept. 15 | Cloudy | 24° /11° | 0 mm | 6 | |
| Sept. 16 |  Thundery outbreaks possible | 24° /10° | 0.4 mm | 5 | |
| Sept. 17 | Thundery outbreaks possible | 25° /12° | 5.3 mm | 5 | |
| Sept. 18 | Overcast | 23° /14° | 2.2 mm | 4 | |
| Sept. 19 | Overcast | 27° /14° | 0 mm | 6 | |
| Sept. 20 | Sunny | 26° /13° | 0 mm | 6 | |
| Sept. 21 | Sunny | 25° /12° | 0 mm | 5 | |
| Sept. 22 | Sunny | 25° /10° | 0 mm | 5 | |
| Sept. 23 | Sunny | 29° /15° | 0 mm | 5.5 | |
| Sept. 24 | Overcast | 34° /18° | 0 mm | 5.4 | |
| Sept. 25 | Overcast | 27° /15° | 0 mm | 4.9 | |
| Sept. 26 | Overcast | 22° /9° | 0 mm | 4.8 | |
| Sept. 27 | Overcast | 23° /12° | 0 mm | 6 | |
| Sept. 28 | Sunny | 18° /10° | 0.7 mm | 5 | |
| Sept. 29 | Overcast | 21° /8° | 0 mm | 5 | |
| Sept. 30 | Sunny | 28° /13° | 0 mm | 7 | |
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Important Notice
Our weather forecast for Ada 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 Ada County forecast closer to your planned date for the most up-to-date weather information.
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Ada County in September - FAQ
What are the expected maximum and minimum temperatures in Ada County during September?
Enjoy moderate daytime temperatures of up to 27° and cooler nights around 14°. Ideal for a range of outdoor activities, from hiking to city tours.
How much rainfall should be expected in Ada County during September?
In September, Ada County can expect light to moderate rainfall, totaling 22.5 mm across approximately 5 days. Occasional showers are possible, and planning ahead for them could be helpful.
What are the typical wind conditions in Ada County during September?
The average wind speed in Ada County during September is 16 km/h, suggesting breezy to windy conditions, depending on your activities.
September rainfall patterns in Ada County
Explore the daily rainfall trends and prepare for Ada Countys September weather 💧
Typically, Ada County has 5 rainy days in September with a total of 22.5 mm of rainfall.
UV exposure in Ada County during September
Stay informed about UV levels for safe outdoor activities throughout the month of September ☀️
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Where is Ada County?Get accurate weather forecasts for Ada County, located at latitude 43.614 and longitude -116.203. Stay updated with localized weather information tailored for Ada County.
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