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September Weather in Forest Grove, United States

Last updated: June 24, 2025

In Forest Grove, United States, the average temperature in September hovers around 17°C (64°F). However, be prepared for a range of temperatures — it can drop as low as 5°C (41°F) or soar up to 34°C (94°F). During this time, precipitation averages 66 mm (2.6 in) over about 8 days, while the air feels quite humid, with an average humidity level of 71%.

September Temperature in Forest Grove

In September in Forest Grove, the average temperature is 17°C (64°F). Maximum temperatures can reach 34°C (94°F), while minimums can drop as low as 5°C (41°F). It’s a great time to explore the outdoors while being prepared for both warm and cool conditions.

September Weather in Forest Grove: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Forest Grove, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Forest Grove, September typically has an average temperature of 17°C (64°F), with highs reaching up to 34°C (94°F) and lows dropping to around 5°C (41°F).
JanFebMarAprMayJunJulAugSepOctNovDec414145515763687063534641
Data source: Temperature data for Forest Grove 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 Forest Grove

In Forest Grove in September, the total precipitation amount is 66 mm (2.6 in) over the course of 8 days.

September Precipitation Trends in Forest Grove

The chart displays monthly precipitation patterns in Forest Grove, 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 Forest Grove, September typically receives around 66 mm (2.6 inches) of precipitation spread over approximately 8 days.
JanFebMarAprMayJunJulAugSepOctNovDec17316613211555476666101163188
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Forest Grove

In Forest Grove in September humidity is 71%. With an average temperature of 17°C (64°F), this humidity feels like a warm, enveloping embrace that can make travel feel a bit sticky, yet still pleasant as you explore the sights with a gentle sheen of perspiration.

September Average Humidity in Forest Grove

This chart illustrates the average monthly humidity levels in Forest Grove, 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 Forest Grove is approximately 71%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec85%84%85%83%83%84%82%74%71%81%87%87%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Forest Grove

In Forest Grove 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 Forest Grove.

Maximum UV Index Levels in Forest Grove for September

The chart shows the monthly maximum UV Index (UVI) for Forest Grove 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 Forest Grove typically reaches 7, which falls under the high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec23579101087532
Data source: Forest Grove 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 Forest Grove Compares to Other Months

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

This table compares monthly weather conditions in Forest Grove, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather5°C (42°F)173 mm (6.8 inches)85%low
February Weather5°C (41°F)166 mm (6.5 inches)84%moderate
March Weather7°C (46°F)132 mm (5.2 inches)85%moderate
April Weather10°C (51°F)115 mm (4.5 inches)83%high
May Weather14°C (58°F)55 mm (2.2 inches)83%very high
June Weather17°C (64°F)47 mm (1.9 inches)83%very high
July Weather20°C (69°F)5 mm (0.2 inches)82%very high
August Weather21°C (70°F)6 mm (0.2 inches)74%very high
September Weather17°C (64°F)66 mm (2.6 inches)71%high
October Weather11°C (53°F)101 mm (4.0 inches)81%moderate
November Weather8°C (46°F)163 mm (6.4 inches)87%moderate
December Weather5°C (41°F)188 mm (7.4 inches)87%low

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