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September Weather in Portland, United States

Last updated: June 24, 2025

In September, the average temperature in Portland, United States is a comfortable 18°C (65°F), though it can vary significantly, with minimums dropping to 1°C (33°F) and maximums soaring to 35°C (94°F). Expect about 108 mm (4.3 in) of precipitation spread over 10 days, contributing to an average humidity of 79%. Ideal for experiencing the diverse climates of this location!

September Temperature in Portland

In September in Portland, the average temperature is 18°C (65°F). The maximum can reach 35°C (94°F), and the minimum can be as low as 1°C (33°F). Be prepared for a wide range of temperatures when traveling, layering your clothing to stay comfortable throughout the day.

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

The chart illustrates September temperature patterns in Portland, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Portland, September typically has an average temperature of 18°C (65°F), with highs reaching up to 35°C (94°F) and lows dropping to around 1°C (33°F).
JanFebMarAprMayJunJulAugSepOctNovDec262737476070757265533832
Data source: Temperature data for Portland 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 Portland

In Portland in September, the total precipitation amount is 108 mm (4.3 in) spread over a duration of 10 days.

September Precipitation Trends in Portland

The chart displays monthly precipitation patterns in Portland, 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 Portland, September typically receives around 108 mm (4.3 inches) of precipitation spread over approximately 10 days.
JanFebMarAprMayJunJulAugSepOctNovDec6771688713610682681081276463
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Portland

In Portland in September, humidity is 79%. With an average temperature of 18°C (65°F), this humidity feels like walking through a warm mist, making traveling slightly uncomfortable and sticky, but offering a refreshing escape when you find moments of shade or a breeze.

September Average Humidity in Portland

This chart illustrates the average monthly humidity levels in Portland, 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 Portland is approximately 79%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec87%87%86%87%82%81%78%79%80%82%87%86%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Portland

In Portland 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 Portland.

Maximum UV Index Levels in Portland for September

The chart shows the monthly maximum UV Index (UVI) for Portland 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 Portland typically reaches 7, which falls under the high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec24589101097532
Data source: Portland 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 Portland Compares to Other Months

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

This table compares monthly weather conditions in Portland, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-3°C (26°F)67 mm (2.6 inches)87%low
February Weather-3°C (27°F)71 mm (2.8 inches)87%moderate
March Weather3°C (37°F)68 mm (2.7 inches)86%moderate
April Weather8°C (47°F)87 mm (3.4 inches)87%very high
May Weather15°C (60°F)136 mm (5.4 inches)82%very high
June Weather21°C (70°F)106 mm (4.2 inches)81%very high
July Weather24°C (75°F)82 mm (3.2 inches)78%very high
August Weather22°C (72°F)68 mm (2.7 inches)79%very high
September Weather18°C (65°F)108 mm (4.3 inches)79%high
October Weather12°C (53°F)127 mm (5.0 inches)82%moderate
November Weather4°C (39°F)64 mm (2.5 inches)87%moderate
December Weather0°C (32°F)63 mm (2.5 inches)86%low

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