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September Weather in Bellevue, United States

Last updated: June 24, 2025

In September, the average temperature in Bellevue, United States is a comfortable 19°C (67°F). However, be prepared for a temperature range that can dip as low as 3°C (37°F) and soar to a sticky 33°C (92°F). Expect around 116 mm (4.6 in) of precipitation over roughly 10 days, contributing to an average humidity of 74%. Stay hydrated and enjoy the climate!

September Temperature in Bellevue

In September in Bellevue, the average temperature is 19°C (67°F). The maximum can reach 33°C (92°F), while the minimum can drop to as low as 3°C (37°F). This makes it a great time to travel for those who enjoy mild weather during the day but can also appreciate refreshing cool nights.

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 19°C (67°F), with highs reaching up to 33°C (92°F) and lows dropping to around 3°C (37°F).
JanFebMarAprMayJunJulAugSepOctNovDec222438476172767266523730
Data source: Temperature data for Bellevue generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Bellevue

In Bellevue in September, the total precipitation amount is 116 mm (4.6 in) 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 116 mm (4.6 inches) of precipitation spread over approximately 10 days.
JanFebMarAprMayJunJulAugSepOctNovDec52596991150129781031161154745
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Bellevue

In Bellevue in September, humidity is 74%. With an average temperature of 19°C (67°F), this humidity feels like a warm, enveloping blanket that can make outdoor activities feel stifling, often leading travelers to seek shade and hydrate frequently.

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 74%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec84%85%84%83%75%79%75%69%74%79%88%82%
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.
JanFebMarAprMayJunJulAugSepOctNovDec34689101098532
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.
 TemperaturePrecipitationHumidityUV
January Weather-6°C (22°F)52 mm (2.1 inches)84%moderate
February Weather-5°C (24°F)59 mm (2.3 inches)85%moderate
March Weather3°C (38°F)69 mm (2.7 inches)84%high
April Weather9°C (48°F)91 mm (3.6 inches)83%very high
May Weather16°C (61°F)150 mm (5.9 inches)75%very high
June Weather22°C (72°F)129 mm (5.1 inches)79%very high
July Weather24°C (76°F)78 mm (3.1 inches)75%very high
August Weather22°C (72°F)103 mm (4.0 inches)69%very high
September Weather19°C (67°F)116 mm (4.6 inches)74%very high
October Weather11°C (52°F)115 mm (4.5 inches)79%moderate
November Weather3°C (37°F)47 mm (1.8 inches)88%moderate
December Weather-1°C (31°F)45 mm (1.8 inches)82%low

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