Sonoma County (Santa Rosa)
September
Weather in Sonoma County, California for September 2026
Your guide to Sonoma County weather in September - trends and predictions
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So far, September 2026 in Sonoma County is slightly warmer than the historical average by 1.3 °F.
The forecast for the upcoming days in Sonoma County predicts a temperature of 30.6 °F, which is slightly above the historical average.
In general, the average temperature in Sonoma County at the beginning of September is 26.3 °F. As the month progressed, temperatures tended to noticeably warm up, reaching an average of 29.3 °F by the end of September.
With an average of 2 rainy days, Sonoma County experiences minimal rainfall in September.
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Temperatures
Rain 🌧️
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28
Dry days
2
Rainy days
0
Snow days
25°/11°
Temperatures
15 km/h
Avg max wind
72 %
Avg humidity
Sonoma County Weather September
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Temperatures trend during September in Sonoma County
See the weather trend as well as the moving average line
September weather in Sonoma County day by day
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| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 |  Mist | 24° /11° | 0 mm | 6 | |
| Sept. 2 |  Patchy rain possible | 24° /11° | 7.9 mm | 5 | |
| Sept. 3 | Mist | 25° /12° | 14.8 mm | 5 | |
| Sept. 4 |  Sunny | 28° /12° | 0 mm | 7 | |
| Sept. 5 | Sunny | 28° /11° | 0 mm | 7 | |
| Sept. 6 | Mist | 27° /10° | 0 mm | 7 | |
| Sept. 7 | Mist | 28° /10° | 0 mm | 7 | |
| Sept. 8 | Sunny | 28° /10° | 0 mm | 7 | |
| Sept. 9 | Mist | 28° /13° | 0 mm | 5 | |
| Sept. 10 |  Cloudy | 26° /12° | 0 mm | 6 | |
| Sept. 11 | Sunny | 27° /11° | 0 mm | 7 | |
| Sept. 12 | Cloudy | 27° /11° | 0 mm | 7 | |
| Sept. 13 | Sunny | 27° /11° | 0 mm | 7 | |
| Sept. 14 | Sunny | 29° /12° | 0 mm | 7 | |
| Sept. 15 | Mist | 27° /11° | 0 mm | 7 | |
| Sept. 16 |  Partly cloudy | 25° /11° | 0 mm | 7 | |
| Sept. 17 | Mist | 24° /11° | 0 mm | 6 | |
| Sept. 18 | Mist | 24° /11° | 3.2 mm | 6 | |
| Sept. 19 | Mist | 25° /12° | 0 mm | 6 | |
| Sept. 20 | Mist | 23° /11° | 0 mm | 4 | |
| Sept. 21 | Sunny | 26° /11° | 0 mm | 6.4 | |
| Sept. 22 | Sunny | 28° /11° | 0 mm | 6.3 | |
| Sept. 23 | Sunny | 32° /14° | 0 mm | 6.4 | |
| Sept. 24 |  Overcast | 29° /15° | 0 mm | 6 | |
| Sept. 25 | Sunny | 29° /13° | 0 mm | 5.9 | |
| Sept. 26 | Sunny | 28° /12° | 0 mm | 7 | |
| Sept. 27 | Sunny | 27° /10° | 0 mm | 7 | |
| Sept. 28 | Sunny | 29° /12° | 0 mm | 7 | |
| Sept. 29 | Sunny | 31° /12° | 0 mm | 8 | |
| Sept. 30 | Sunny | 32° /15° | 0 mm | 8 | |
| Next | |||||
Important Notice
Our weather forecast for Sonoma 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 Sonoma County forecast closer to your planned date for the most up-to-date weather information.
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Sonoma County in September - FAQ
What are the expected maximum and minimum temperatures in Sonoma County during September?
Enjoy moderate daytime temperatures of up to 25° and cooler nights around 11°. Ideal for a range of outdoor activities, from hiking to city tours.
How much rainfall should be expected in Sonoma County during September?
Rainfall in Sonoma County during September is rare to nonexistent, with the total expected rainfall being less than 10 mm and approximately 2 days seeing any precipitation. Planning without the concern for rain is generally straightforward during this very dry period.
What are the typical wind conditions in Sonoma County during September?
The average wind speed in Sonoma County during September is 15 km/h, suggesting breezy to windy conditions, depending on your activities.
September rainfall patterns in Sonoma County
Explore the daily rainfall trends and prepare for Sonoma Countys September weather 💧
Typically, Sonoma County has 2 rainy days in September with a total of 6.6 mm of rainfall.
UV exposure in Sonoma County during September
Stay informed about UV levels for safe outdoor activities throughout the month of September ☀️
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