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Weather in Sonoma County for September 2025

Your guide to Sonoma County weather in September - trends and predictions
  • In general, the average temperature in Sonoma County at the beginning of September is 27.3 °F. As the month progressed, temperatures tended to moderately fall, reaching an average of 25.4 °F by the end of September.

  • With an average of 2 rainy days, Sonoma County experiences minimal rainfall in September.

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Average dry days
28
Dry days
Average rainy days
2
Rainy days
Average snowy days
0
Snow days
Average temperatures
25°/10°
Temperatures
Average wind speed
15 km/h
Avg max wind
Average humidity
73 %
Avg humidity

Sonoma County in September average weather

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Temperatures trend during September in Sonoma County

See the weather trend as well as the moving average line

September weather day by day

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Date Weather Temperatures Rain UV More
Sept. 1 Mist
Mist
23° /11° 0 mm 6
Sept. 2 Patchy rain possible
Patchy rain possible
23° /11° 0.1 mm 6
Sept. 3 Mist
Mist
29° /11° 0 mm 7
Sept. 4 Partly cloudy
Partly cloudy
31° /13° 0 mm 8
Sept. 5 Cloudy
Cloudy
31° /12° 0 mm 7
Sept. 6 Mist
Mist
28° /10° 0 mm 7
Sept. 7 Mist
Mist
26° /9° 0 mm 7
Sept. 8 Overcast
Overcast
27° /10° 0 mm 7
Sept. 9 Mist
Mist
28° /9° 0 mm 7
Sept. 10 Cloudy
Cloudy
26° /9° 0 mm 6
Sept. 11 Sunny
Sunny
28° /10° 0 mm 8
Sept. 12 Cloudy
Cloudy
27° /10° 0 mm 7
Sept. 13 Partly cloudy
Partly cloudy
29° /11° 0 mm 8
Sept. 14 Mist
Mist
27° /11° 0 mm 7
Sept. 15 Mist
Mist
24° /10° 0 mm 6
Sept. 16 Mist
Mist
23° /10° 0 mm 6
Sept. 17 Mist
Mist
21° /10° 0 mm 5
Sept. 18 Mist
Mist
23° /11° 0 mm 5
Sept. 19 Mist
Mist
22° /12° 0 mm 6
Sept. 20 Mist
Mist
21° /10° 0 mm 5
Sept. 21 Partly cloudy
Partly cloudy
23° /9° 0 mm 6
Sept. 22 Mist
Mist
26° /8° 0 mm 6
Sept. 23 Mist
Mist
28° /9° 0 mm 7
Sept. 24 Mist
Mist
27° /10° 0 mm 7
Sept. 25 Patchy rain possible
Patchy rain possible
20° /9° 0.6 mm 5
Sept. 26 Mist
Mist
25° /11° 2.7 mm 6
Sept. 27 Sunny
Sunny
30° /10° 0 mm 8
Sept. 28 Partly cloudy
Partly cloudy
24° /9° 0 mm 6
Sept. 29 Cloudy
Cloudy
26° /10° 0 mm 6
Sept. 30 Patchy rain possible
Patchy rain possible
26° /11° 0 mm 7
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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.

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 10°. 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 💧

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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Location coordinates Where is Sonoma County?

Get accurate weather forecasts for Sonoma County, located at latitude 38.44 and longitude -122.714. Stay updated with localized weather information tailored for Sonoma County.

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