King County (Seattle)
September
Weather in King County, Washington for September 2026
Your guide to King County weather in September - trends and predictions
Until now, September 2026 in King County is cooler than usual, with temperatures averaging 20.3 °F, this is 2.1 °F below the typical seasonal average.
The forecast for the coming days of September 2026 predicts a temperature of 20.6 °F , which is warmer than usual.
In general, the average temperature in King County at the beginning of September is 25.3 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 18.3 °F by the end of September.
King County experiences moderate rainfall in September, with an average of 6 rainy days and a total precipitation of 50.4 mm.
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Temperatures
Rain 🌧️
More
24
Dry days
6
Rainy days
0
Snow days
22°/11°
Temperatures
11 km/h
Avg max wind
70 %
Avg humidity
King County Weather September
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Temperatures trend during September in King County
See the weather trend as well as the moving average line
September weather in King County day by day
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| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 |  Partly cloudy | 25° /13° | 0 mm | 6 | |
| Sept. 2 |  Overcast | 26° /12° | 4.2 mm | 6 | |
| Sept. 3 | Overcast | 24° /12° | 0.5 mm | 5 | |
| Sept. 4 |  Mist | 25° /12° | 0.2 mm | 6 | |
| Sept. 5 | Overcast | 26° /13° | 0.2 mm | 6 | |
| Sept. 6 |  Sunny | 26° /12° | 0.5 mm | 6 | |
| Sept. 7 | Partly cloudy | 25° /12° | 0 mm | 6 | |
| Sept. 8 | Partly cloudy | 25° /12° | 0.1 mm | 6 | |
| Sept. 9 | Overcast | 24° /12° | 0 mm | 5 | |
| Sept. 10 | Overcast | 25° /12° | 0 mm | 5 | |
| Sept. 11 | Overcast | 20° /13° | 0.7 mm | 4 | |
| Sept. 12 |  Patchy rain possible | 21° /12° | 1.2 mm | 4 | |
| Sept. 13 | Mist | 20° /11° | 2.9 mm | 5 | |
| Sept. 14 | Patchy rain possible | 21° /10° | 2.1 mm | 4 | |
| Sept. 15 | Patchy rain possible | 21° /10° | 1 mm | 5 | |
| Sept. 16 | Overcast | 23° /9° | 0.5 mm | 5 | |
| Sept. 17 | Overcast | 20° /11° | 4.2 mm | 5 | |
| Sept. 18 | Overcast | 19° /10° | 1.9 mm | 4 | |
| Sept. 19 | Overcast | 20° /10° | 2.4 mm | 5 | |
| Sept. 20 |  Cloudy | 21° /9° | 0.8 mm | 5 | |
| Sept. 21 | Partly cloudy | 21° /8° | 0.5 mm | 5 | |
| Sept. 22 | Overcast | 21° /10° | 0 mm | 5 | |
| Sept. 23 | Overcast | 21° /12° | 1 mm | 4 | |
| Sept. 24 | Sunny | 21° /10° | 3 mm | 5 | |
| Sept. 25 | Sunny | 19° /10° | 6 mm | 4 | |
| Sept. 26 |  Moderate rain at times | 19° /10° | 6.2 mm | 4 | |
| Sept. 27 | Overcast | 18° /8° | 0 mm | 3.5 | |
| Sept. 28 | Overcast | 19° /8° | 0 mm | 3.8 | |
| Sept. 29 |  Light drizzle | 14° /12° | 4.8 mm | 0.4 | |
| Sept. 30 | Overcast | 18° /10° | 0.2 mm | 3.4 | |
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Important Notice
Our weather forecast for King 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 King County forecast closer to your planned date for the most up-to-date weather information.
Change Month
King County in September - FAQ
What are the expected maximum and minimum temperatures in King County during September?
Enjoy moderate daytime temperatures of up to 22° and cooler nights around 11°. Ideal for a range of outdoor activities, from hiking to city tours.
How much rainfall should be expected in King County during September?
Moderate rainfall is anticipated in King County during September, with a total of 50.4 mm spread over approximately 6 days. Considering plans for rainy days is advisable.
What are the typical wind conditions in King County during September?
The average wind speed in King County during September is 11 km/h, suggesting breezy to windy conditions, depending on your activities.
September rainfall patterns in King County
Explore the daily rainfall trends and prepare for King Countys September weather 💧
Typically, King County has 6 rainy days in September with a total of 50.4 mm of rainfall.
UV exposure in King County during September
Stay informed about UV levels for safe outdoor activities throughout the month of September ☀️
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Where is King County?Get accurate weather forecasts for King County, located at latitude 47.606 and longitude -122.332. Stay updated with localized weather information tailored for King County.
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