Weather in King County, Washington for September 2025
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Until now, September 2025 in King County is slightly cooler than the historical average by -1.8 °F.
Expect cooler weather in the next days in King County with the forecast suggesting a temperature of 21.7 °F, lower than the historical average.
In general, the average temperature in King County at the beginning of September is 25.7 °F. As the month progressed, temperatures tended to significantly cool down, reaching an average of 17.9 °F by the end of September.
The climate of King County in September is notably wet, with an average of 14 rainy days, and a total of 55.2 mm of precipitation.
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King County Weather September
Temperatures trend during September in King County
September weather in King County day by day
| Date | Weather | Temperatures | Rain | UV | More |
|---|---|---|---|---|---|
| Sept. 1 |  Partly cloudy | 25° /12° | 0 mm | 6 | |
| Sept. 2 |  Sunny | 27° /12° | 0 mm | 7 | |
| Sept. 3 |  Overcast | 25° /13° | 0 mm | 6 | |
| Sept. 4 |  Mist | 25° /12° | 0.2 mm | 6 | |
| Sept. 5 | Overcast | 27° /14° | 0.3 mm | 7 | |
| Sept. 6 | Sunny | 26° /12° | 0.6 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 | 6 | |
| Sept. 10 |  Patchy rain possible | 25° /11° | 0 mm | 6 | |
| Sept. 11 | Overcast | 20° /13° | 0.9 mm | 5 | |
| Sept. 12 | Patchy rain possible | 21° /12° | 0.6 mm | 5 | |
| Sept. 13 | Mist | 21° /11° | 0.2 mm | 5 | |
| Sept. 14 | Patchy rain possible | 21° /10° | 2.5 mm | 5 | |
| Sept. 15 | Partly cloudy | 21° /14° | 0 mm | 1.2 | |
| Sept. 16 | Sunny | 34° /13° | 0 mm | 1.1 | |
| Sept. 17 | Sunny | 27° /16° | 0 mm | 1.2 | |
| Sept. 18 | Partly cloudy | 23° /12° | 0 mm | 1.1 | |
| Sept. 19 | Sunny | 25° /11° | 0 mm | 0 | |
| Sept. 20 | Patchy rain possible | 15° /10° | 0.2 mm | 3 | |
| Sept. 21 | Patchy rain possible | 22° /13° | 0.1 mm | 4 | |
| Sept. 22 | Patchy rain possible | 22° /12° | 0.3 mm | 4 | |
| Sept. 23 | Sunny | 24° /10° | 0 mm | 5 | |
| Sept. 24 | Patchy rain possible | 21° /13° | 2.7 mm | 3 | |
| Sept. 25 | Partly cloudy | 19° /11° | 0 mm | 4 | |
| Sept. 26 | Partly cloudy | 16° /8° | 0 mm | 4 | |
| Sept. 27 | Sunny | 21° /9° | 0 mm | 4 | |
| Sept. 28 |  Moderate rain | 14° /11° | 8.9 mm | 3 | |
| Sept. 29 |  Moderate rain at times | 17° /9° | 0.8 mm | 4 | |
| Sept. 30 | Moderate or heavy rain shower | 17° /7° | 4.5 mm | 4 | |
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King County in September - FAQ
September rainfall patterns in King County
UV exposure in King County during 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.