September Weather in Washington, United States

Last updated: June 24, 2025

In September, the average temperature in Washington, United States hovers around 22°C (72°F), offering a pleasant climate. However, temperatures can fluctuate, with a minimum of 7°C (46°F) and a maximum reaching 34°C (93°F). Expect about 71 mm (2.8 in) of precipitation spread over 8 days, contributing to an average humidity of 69%.

September Temperature in Washington

In September in Washington, the average temperature is 22°C (72°F). Maximums can reach 34°C (93°F) and minimums can drop to as low as 7°C (46°F). Travelers should pack a variety of clothing to accommodate both warm days and cool evenings.

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 22°C (72°F), with highs reaching up to 34°C (93°F) and lows dropping to around 7°C (46°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 71 mm (2.8 in) over the course of 8 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 71 mm (2.8 inches) of precipitation spread over approximately 8 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 69%. With an average temperature of 22°C (72°F), this humidity feels like a warm, enveloping blanket, making travel feel sticky and slightly oppressive, yet also invigorating as the air is thick with the scent of blooming flora and vibrant surroundings.

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 69%, 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 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to 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 8, which falls under the very 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	1°C (33°F)	93 mm (3.7 inches)	87%	moderate
February Weather	3°C (37°F)	114 mm (4.5 inches)	85%	moderate
March Weather	8°C (47°F)	139 mm (5.5 inches)	86%	high
April Weather	13°C (55°F)	123 mm (4.8 inches)	84%	very high
May Weather	20°C (67°F)	133 mm (5.2 inches)	79%	very high
June Weather	24°C (76°F)	118 mm (4.6 inches)	82%	extreme
July Weather	26°C (79°F)	89 mm (3.5 inches)	79%	very high
August Weather	24°C (76°F)	91 mm (3.6 inches)	70%	very high
September Weather	22°C (72°F)	71 mm (2.8 inches)	69%	very high
October Weather	16°C (60°F)	97 mm (3.8 inches)	76%	high
November Weather	7°C (44°F)	102 mm (4.0 inches)	88%	moderate
December Weather	4°C (39°F)	104 mm (4.1 inches)	87%	moderate