September Weather in Bellevue, United States

Last updated: June 24, 2025

In September, the average temperature in Bellevue, United States hovers around 20°C (68°F), creating a mild and enjoyable climate. Temperatures can vary significantly, with a minimum of 5°C (40°F) and a maximum reaching up to 34°C (93°F). Expect about 128 mm (5.0 in) of precipitation spread over 10 days, contributing to an average humidity of 77%.

September Temperature in Bellevue

In September in Bellevue, the average temperature is 20°C (68°F), with maximums reaching up to 34°C (93°F) and minimums dropping as low as 5°C (40°F). It's a great time to visit for those who enjoy mild weather with the option of some warm days.

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

The chart illustrates September temperature patterns in Bellevue, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Bellevue, September typically has an average temperature of 20°C (68°F), with highs reaching up to 34°C (93°F) and lows dropping to around 5°C (40°F).

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

September Precipitation in Bellevue

In Bellevue in September, the total precipitation amount is 128 mm (5.0 in) recorded over a span of 10 days.

September Precipitation Trends in Bellevue

The chart displays monthly precipitation patterns in Bellevue, 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 Bellevue, September typically receives around 128 mm (5.0 inches) of precipitation spread over approximately 10 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 Bellevue

In Bellevue in September, humidity is 77%. With an average temperature of 20°C (68°F), this humidity feels like a warm, sticky embrace, making it essential for travelers to stay hydrated and take breaks in shaded areas to avoid feeling sluggish in the heat.

September Average Humidity in Bellevue

This chart illustrates the average monthly humidity levels in Bellevue, 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 Bellevue 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 Bellevue

In Bellevue 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 Bellevue.

Maximum UV Index Levels in Bellevue for September

The chart shows the monthly maximum UV Index (UVI) for Bellevue 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 Bellevue typically reaches 8, which falls under the very high exposure category.

Data source: Bellevue 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 Bellevue Compares to Other Months

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

This table compares monthly weather conditions in Bellevue, 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 (31°F)	95 mm (3.7 inches)	88%	moderate
February Weather	1°C (35°F)	125 mm (4.9 inches)	88%	moderate
March Weather	5°C (42°F)	109 mm (4.3 inches)	87%	high
April Weather	11°C (52°F)	132 mm (5.2 inches)	87%	very high
May Weather	17°C (63°F)	150 mm (5.9 inches)	81%	very high
June Weather	21°C (70°F)	155 mm (6.1 inches)	83%	very high
July Weather	24°C (75°F)	154 mm (6.1 inches)	82%	very high
August Weather	23°C (73°F)	89 mm (3.5 inches)	76%	very high
September Weather	20°C (68°F)	128 mm (5.0 inches)	77%	very high
October Weather	14°C (57°F)	128 mm (5.0 inches)	82%	high
November Weather	5°C (42°F)	94 mm (3.7 inches)	89%	moderate
December Weather	2°C (36°F)	102 mm (4.0 inches)	86%	low