September Weather in Portland, United States

Last updated: June 24, 2025

In Portland, United States, the average temperature in September is a pleasant 15°C (60°F). However, temperatures can vary significantly, with a minimum of -2°C (28°F) and a maximum of 32°C (90°F). Be prepared for some moisture, as there’s an expected precipitation amount of 68 mm (2.7 in) over approximately 7 days. Additionally, the average humidity hovers around 77%, making for potentially muggy conditions.

September Temperature in Portland

In September, in Portland, the average temperature is 15°C (60°F). Maximums can reach up to 32°C (90°F), while minimums can plummet to as low as -2°C (28°F). Be prepared for a mix of warm and chilly weather, making it essential to pack accordingly for your trip.

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 15°C (60°F), with highs reaching up to 32°C (90°F) and lows dropping to around -2°C (28°F).

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

September Precipitation in Portland

In Portland in September, the precipitation amount is 68 mm (2.7 in) over the course of 7 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 68 mm (2.7 inches) of precipitation spread over approximately 7 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 Portland

In Portland in September, humidity is 77%. With an average temperature of 15°C (60°F), this humidity feels like you're wading through a warm, heavy blanket, making travel feel more exhausting and sticky than usual.

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 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 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.

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.
	Temperature	Precipitation	Humidity	UV
January Weather	-12°C (10°F)	18 mm (0.7 inches)	90%	low
February Weather	-13°C (9°F)	19 mm (0.8 inches)	92%	moderate
March Weather	-3°C (27°F)	27 mm (1.1 inches)	85%	moderate
April Weather	4°C (39°F)	41 mm (1.6 inches)	81%	high
May Weather	13°C (56°F)	55 mm (2.2 inches)	75%	very high
June Weather	20°C (69°F)	91 mm (3.6 inches)	79%	very high
July Weather	22°C (72°F)	62 mm (2.4 inches)	76%	very high
August Weather	20°C (68°F)	81 mm (3.2 inches)	78%	very high
September Weather	15°C (60°F)	68 mm (2.7 inches)	77%	high
October Weather	6°C (44°F)	79 mm (3.1 inches)	79%	moderate
November Weather	-2°C (28°F)	21 mm (0.8 inches)	86%	moderate
December Weather	-8°C (18°F)	39 mm (1.5 inches)	86%	low