September Weather in Washington, United States

Last updated: June 24, 2025

In September, the average temperature in Washington, United States is a pleasant 17°C (62°F). You can expect temperatures to range from a cool 4°C (40°F) to a warm 28°C (83°F). With 83 mm (3.2 in) of precipitation spread over 9 days, be prepared for occasional showers. The average humidity during this time is around 77%, adding a touch of humidity to the air.

September Temperature in Washington

In September in Washington, the average temperature is 17°C (62°F). Maximum temperatures can reach 28°C (83°F), while minimums can drop to as low as 4°C (40°F). Be sure to pack layers to comfortably enjoy the variety of weather during your travels!

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 28°C (83°F) and lows dropping to around 4°C (40°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 83 mm (3.2 in) spread over a period of 9 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 83 mm (3.2 inches) of precipitation spread over approximately 9 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 77%. With an average temperature of 17°C (62°F), this humidity feels like a warm embrace, creating a lush, almost tropical atmosphere that can be quite stifling for traveling, making it essential to stay hydrated and take frequent breaks in the shade.

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 77%, 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	-3°C (26°F)	97 mm (3.8 inches)	88%	low
February Weather	-3°C (27°F)	95 mm (3.7 inches)	88%	moderate
March Weather	0°C (33°F)	78 mm (3.1 inches)	85%	moderate
April Weather	6°C (43°F)	141 mm (5.6 inches)	81%	high
May Weather	11°C (53°F)	92 mm (3.6 inches)	76%	very high
June Weather	17°C (62°F)	72 mm (2.8 inches)	74%	very high
July Weather	20°C (68°F)	102 mm (4.0 inches)	74%	very high
August Weather	20°C (68°F)	81 mm (3.2 inches)	74%	very high
September Weather	17°C (62°F)	83 mm (3.2 inches)	77%	high
October Weather	11°C (52°F)	143 mm (5.6 inches)	82%	moderate
November Weather	4°C (40°F)	121 mm (4.8 inches)	85%	moderate
December Weather	-1°C (30°F)	135 mm (5.3 inches)	84%	low