Portland Weather in September

Portland's pleasant summer weather continues into September with relatively sunny and dry conditions along with moderate temperatures.

This page gives detailed information on the typical September temperature, precipitation, sun, humidity, wind and storms for Portland Oregon. The numbers here are historical averages based on climate data gathered near the Portland International Airport, located a few miles from downtown Portland.

Temperature Weather iconTemperature

76 °F September average high 24 °C
53 °F September average low 12 °C
10 days 80 °F max. or more (27 °C)
9 days 50 °F min. or less (10 °C)

Usually every day in September warms to over 60 degrees Fahrenheit (16 degrees Celsius) in Portland. The city averages 2 days this month when the thermometer reaches into the 90s °F (over 32 °C). Temperatures above 100 °F (38 °C) are not expected here during September.

At night, the thermometer dips down to 40 °F (40°C) or below about once a decade. September does not normally get cold enough for frost.

Rainy Weather iconRain

1.7 in total precipitation 42 mm
7 days of rain

Half the time, Portland receives 1.0 to 2.0 inches (26 to 50 mm) of rainfall in September. One in four years has drier weather, while another one in four is wetter.

Sunny Weather iconSun

62 % sunshine
10 days clear skies

The sun's rays reach the ground in Portland during 62 percent of daylight hours on average in September, for a total of 233 hours in the month. Typically on 10 days this month the sky is mainly clear, with at most 30 percent cloud cover.

Sunlight in September at Portland lasts for 12 hours and 29 minutes a day on average. The longest day of the month is the 1st with 13 hours and 15 minutes of daylight. By the end of the month, the days have shortened to 11:44 from sunrise to sunset. These durations can vary by a minute or two from year to year.

Humid Weather iconHumidity

69 % September average humidity

The relative humidity in Portland during September usually peaks at 86 percent in the morning then drops to 48 percent by mid afternoon.

Local Time1 am4 am7 am10 am1 pm4 pm7 pm10 pm
Humidity % 81 86 86 67 52 48 61 74

Windy Weather iconWind

6.5 mph September wind speed average 10.5 kph

September is one of the least windy months in Portland.

Stormy Weather iconStorms

1 day rainfall of 0.5 inches (13 mm) or more
1 day with thunderstorms in September

About once a decade, a storm soaks Portland in an inch (25 mm) or more of rain in one day during September. A September thunderstorm happens in most, but not all, years.


The weather data here are long-term averages provided by the US National Centers for Environmental Information (NCEI). Temperature and precipitation are 1991-2020 normals while humidity and thunderstorms are 1961-1990 normals.

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