September Weather in Washington, United States

Last updated: June 24, 2025

In September, the average temperature in Washington, United States hovers around 17°C (63°F). Expect a minimum of 1°C (35°F) and a peak of 31°C (89°F), making for quite the temperature range. During this month, the area typically sees about 129 mm (5.1 in) of precipitation spread across 9 days, contributing to an average humidity level of 72%. Whether you're planning a visit or just curious, these weather patterns set the stage for an intriguing month!

September Temperature in Washington

In September in Washington, the average temperature is 17°C (63°F). Maximum temperatures can reach as high as 31°C (89°F), while the minimum can drop to a chilly 1°C (35°F). Be sure to pack layers to stay comfortable while exploring the diverse weather conditions!

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 (63°F), with highs reaching up to 31°C (89°F) and lows dropping to around 1°C (35°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 total precipitation amount is 129 mm (5.1 in) over the course 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 129 mm (5.1 inches) of precipitation spread over approximately 9 days.

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

Choose your preferred precipitation unit

Millimeters (mm) Inches (in)

September Humidity in Washington

In Washington in September, humidity is 72%. With an average temperature of 17°C (63°F), this humidity feels like a muggy embrace, making outdoor activities a bit sticky and requiring plenty of hydration for a comfortable travel experience.

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 72%, 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	-4°C (26°F)	86 mm (3.4 inches)	89%	moderate
February Weather	-2°C (29°F)	104 mm (4.1 inches)	88%	moderate
March Weather	1°C (34°F)	90 mm (3.6 inches)	86%	high
April Weather	8°C (46°F)	157 mm (6.2 inches)	84%	very high
May Weather	14°C (57°F)	121 mm (4.8 inches)	76%	very high
June Weather	19°C (67°F)	109 mm (4.3 inches)	72%	very high
July Weather	22°C (72°F)	182 mm (7.1 inches)	66%	very high
August Weather	21°C (70°F)	143 mm (5.6 inches)	64%	very high
September Weather	17°C (63°F)	129 mm (5.1 inches)	72%	very high
October Weather	11°C (53°F)	174 mm (6.9 inches)	81%	high
November Weather	4°C (39°F)	106 mm (4.2 inches)	87%	moderate
December Weather	-1°C (30°F)	130 mm (5.1 inches)	84%	low