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Weather in King County for September 2025

Your guide to King County weather in September - trends and predictions
  • 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 17 °F by the end of September.

  • King County sees moderate rainfall in September, averaging 7 rainy days.

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Average dry days
23
Dry days
Average rainy days
7
Rainy days
Average snowy days
0
Snow days
Average temperatures
21°/10°
Temperatures
Average wind speed
11 km/h
Avg max wind
Average humidity
71 %
Avg humidity

King County in September average weather

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Temperatures trend during September in King 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
27° /12° 0 mm 7
Sept. 2 Sunny
Sunny
28° /13° 0 mm 7
Sept. 3 Patchy rain possible
Patchy rain possible
22° /14° 0.1 mm 5
Sept. 4 Overcast
Overcast
22° /11° 0 mm 5
Sept. 5 Overcast
Overcast
26° /12° 0 mm 7
Sept. 6 Cloudy
Cloudy
26° /11° 0 mm 6
Sept. 7 Partly cloudy
Partly cloudy
26° /11° 0 mm 7
Sept. 8 Partly cloudy
Partly cloudy
26° /11° 0 mm 6
Sept. 9 Mist
Mist
24° /11° 0 mm 6
Sept. 10 Overcast
Overcast
25° /11° 0 mm 6
Sept. 11 Overcast
Overcast
18° /13° 1.5 mm 4
Sept. 12 Overcast
Overcast
20° /11° 0.1 mm 5
Sept. 13 Overcast
Overcast
21° /10° 0.1 mm 5
Sept. 14 Mist
Mist
23° /10° 1.7 mm 5
Sept. 15 Mist
Mist
22° /9° 0 mm 5
Sept. 16 Overcast
Overcast
24° /8° 0 mm 6
Sept. 17 Cloudy
Cloudy
19° /11° 0.8 mm 5
Sept. 18 Patchy rain possible
Patchy rain possible
17° /11° 0.1 mm 4
Sept. 19 Overcast
Overcast
17° /11° 0 mm 4
Sept. 20 Light rain shower
Light rain shower
18° /9° 2.5 mm 4
Sept. 21 Partly cloudy
Partly cloudy
20° /7° 0 mm 6
Sept. 22 Sunny
Sunny
23° /9° 0 mm 6
Sept. 23 Light rain
Light rain
22° /13° 2.9 mm 5
Sept. 24 Light rain
Light rain
21° /10° 4.9 mm 5
Sept. 25 Moderate or heavy rain with thunder
Moderate or heavy rain with thunder
18° /12° 11.6 mm 4
Sept. 26 Moderate or heavy rain with thunder
Moderate or heavy rain with thunder
17° /10° 14.2 mm 4
Sept. 27 Moderate rain
Moderate rain
17° /10° 4.7 mm 4
Sept. 28 Light rain shower
Light rain shower
15° /9° 4.7 mm 4
Sept. 29 Mist
Mist
15° /7° 0 mm 4
Sept. 30 Mist
Mist
16° /6° 0 mm 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.

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 21° and cooler nights around 10°. 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 79.9 mm spread over approximately 7 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 💧

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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Location coordinates 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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