September Weather in Washington, United States

Last updated: June 24, 2025

In September, the average temperature in Washington, United States is a mild 17°C (62°F). Expect a minimum of 7°C (45°F) and a maximum of 23°C (74°F). This month also sees about 85 mm (3.4 in) of precipitation spread over 10 days, with an average humidity of 79%. Be prepared for a mix of pleasant warmth and occasional dampness!

September Temperature in Washington

In September in Washington, the average temperature is 17°C (62°F), with maximums reaching 23°C (74°F) and minimums dropping as low as 7°C (45°F). This makes it a perfect time for travelers who enjoy mild weather and outdoor activities.

September Weather in Washington: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Washington, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Washington, September typically has an average temperature of 17°C (62°F), with highs reaching up to 23°C (74°F) and lows dropping to around 7°C (45°F).

Data source: Temperature data for Washington generated using information from the Copernicus Climate Change Service.

September Precipitation in Washington

In Washington in September, the precipitation amount is 85 mm (3.4 in) over the course of 10 days.

September Precipitation Trends in Washington

The chart displays monthly precipitation patterns in Washington, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Washington, September typically receives around 85 mm (3.4 inches) of precipitation spread over approximately 10 days.

Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.

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Millimeters (mm) Inches (in)

September Humidity in Washington

In Washington in September humidity is 79%. With an average temperature of 17°C (62°F), this humidity feels like a warm blanket wrapping around you, making strolling through the streets a bit heavier but still comfortably refreshing for travelers.

September Average Humidity in Washington

This chart illustrates the average monthly humidity levels in Washington, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Washington is approximately 79%, offering insight into how humid the weather typically is during this month.

Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Washington

In Washington in September, the maximum UV index is 7, which corresponds to the high Exposure Category. This means that the time to burn is approximately 25 minutes. For more detailed information, you can check the Hourly UV Index in Washington.

Maximum UV Index Levels in Washington for September

The chart shows the monthly maximum UV Index (UVI) for Washington in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in Washington typically reaches 7, which falls under the high exposure category.

Data source: Washington September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

Extreme (11+): Avoid the sun, stay in shade.
Very High (8-10): Limit sun exposure.
High (6-7): Use SPF 30+ and protective clothing.
Moderate (3-5): Midday shade recommended.
Low (0-2): No protection needed.

How September Weather in Washington Compares to Other Months

Weather in Washington varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Washington, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Washington, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	-5°C (24°F)	44 mm (1.7 inches)	91%	low
February Weather	-5°C (23°F)	56 mm (2.2 inches)	91%	moderate
March Weather	-1°C (30°F)	61 mm (2.4 inches)	87%	moderate
April Weather	2°C (36°F)	90 mm (3.5 inches)	87%	high
May Weather	7°C (45°F)	83 mm (3.3 inches)	82%	very high
June Weather	14°C (57°F)	90 mm (3.5 inches)	79%	very high
July Weather	20°C (68°F)	76 mm (3.0 inches)	75%	very high
August Weather	20°C (68°F)	87 mm (3.4 inches)	76%	very high
September Weather	17°C (62°F)	85 mm (3.4 inches)	79%	high
October Weather	11°C (51°F)	114 mm (4.5 inches)	83%	moderate
November Weather	3°C (38°F)	67 mm (2.6 inches)	86%	moderate
December Weather	-1°C (30°F)	70 mm (2.8 inches)	87%	low