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 weather for Portland Oregon.

You can jump directly to data and descriptions for:

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

75 °F September average high 24 °C
52 °F September average low 11 °C

In most years, Portland averages a daily maximum temperature for September that's between 73 and 78 degrees Fahrenheit (23 to 26 degrees Celsius). The minimum temperature usually falls between 50 and 54 °F (10 to 12 °C).

The days at Portland begin to cool down quickly during September. By the end of the month, the temperature has dropped around 9 °F (5 °C) below what it was at the start.

9 days 80 °F max. or more (27 °C)
10 days 50 °F min. or less (10 °C)

Nearly every day in September warms to over 60 °F (16 °C) in Portland. The city averages 1 day 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

1.6 in total precipitation 40 mm
7 days of rain

Half the time, Portland receives 0.8 to 2 inches (20 to 51 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.


These weather data are long-term historical averages provided by the National Climatic Data Center of the United States. The temperature and precipitation numbers are 1981-2010 normals while the humidity and thunderstorm statistics are 1961-1990 normals.

Portland Weather
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