September weather forecastPortland, OR
September
Weather in September
Localized weather patterns carry Portland from the hot, dry months of summer into the cool, wet months of fall in September. Registering 1.69" (43mm) of rainfall, the city sees a gradual increase in precipitation. Days start getting shorter, although they still remain long enough for outdoor activities. The weather begins to turn breezier and more comfortable, which signals the onset of autumn. September also brings stunning foliage changes, known to be some of the most impressive in Oregon.Temperature
In Portland, entering September brings a subtle temperature decrement, reducing from August's moderately hot 81.5°F (27.5°C) to a still warm 74.1°F (23.4°C). Portland marks a considerable descent from the daytime apex, as the average temperature dips to a cool 51.3°F (10.7°C) at night throughout September.Humidity
The average relative humidity in September is 69%.Rainfall
In Portland, in September, it is raining for 10.4 days, with typically 1.69" (43mm) of accumulated precipitation. Throughout the year, there are 173.1 rainfall days, and 31.18" (792mm) of precipitation is accumulated.Snowfall
April through October are months without snowfall.Daylight
In September, the average length of the day is 12h and 31min.On the first day of the month, sunrise is at 6:33 am and sunset at 7:47 pm. On the last day of September, sunrise is at 7:08 am and sunset at 6:52 pm PDT.
Sunshine
In September, the average sunshine is 9.3h.UV index
In September, the average daily maximum UV index is 4. A UV Index estimate of 3 to 5 represents a moderate health risk from unsafe exposure to UV radiation for ordinary individuals.Note: In September, the maximum UV index of 4 transforms into these recommendations:
Prioritize safety - Suggestions to prevent sun damage are offered. The most potent solar radiation is around mid-day, so one should minimize exposure to direct sunlight during this period. Consider a wide-brim hat essential for effective sun defense covering your face, neck, and eyes.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in September
Portland, OR
- Average high temperature in September: 74.1°F
The warmest month (with the highest average high temperature) is August (81.5°F).
The month with the lowest average high temperature is December (44.1°F).
- Average low temperature in September: 51.3°F
The month with the highest average low temperature is August (55°F).
The coldest month (with the lowest average low temperature) is December (34.7°F).
Average pressure in September
Portland, OR
- Average pressure in September: 30.01"Hg
The month with the highest atmospheric pressure is January (30.12"Hg).
The month with the lowest atmospheric pressure is August (30"Hg).
Average wind speed in September
Portland, OR
- Average wind speed in September: 4mph
The windiest month (with the highest average wind speed) is January (5.8mph).
The calmest month (with the lowest average wind speed) is August (3.9mph).
Average humidity in September
Portland, OR
- Average humidity in September: 69%
The months with the highest relative humidity are January, February and December (83%).
The month with the lowest relative humidity is August (63%).
Average rainfall in September
Portland, OR
- Average rainfall in September: 1.69"
The wettest month (with the highest rainfall) is December (4.53").
The driest month (with the least rainfall) is July (0.31").
Average rainfall days in September
Portland, OR
- Average rainfall days in September: 10.4 days
The month with the highest number of rainy days is March (20.4 days).
The month with the least rainy days is July (4.9 days).
Average snowfall in September
Portland, OR
- Average snowfall in September: 0"
The month with the highest snowfall is March (1.5").
The months with the least snowfall are April, May, June, July, August, September and October (0").
Average snowfall days in September
Portland, OR
- Average snowfall days in September: 0 days
The month with the highest number of snowfall days is February (2.3 days).
The months with the least snowfall days are May, June, July, August, September and October (0 days).
Average daylight in September /
Average sunshine in September
Portland, OR
- Average daylight in September: 12h and 30min
The month with the longest days is June (Average daylight: 15h and 36min).
The month with the shortest days is December (Average daylight: 8h and 48min).
- Average sunshine in September: 9h and 18min
The month with the most sunshine is August (Average sunshine: 10h and 54min).
The month with the least sunshine is January (Average sunshine: 4h and 6min).
Average sunshine days in September
Portland, OR
- Average sunshine days in September: 17.4 days
The months with the most sunshine days are July and August (23.8 days).
The month with the least sunshine days is March (8.3 days).
Average UV index in September
Portland, OR
- Average UV index in September: 4
The month with the highest UV index is July (UV index 6).
The months with the lowest UV index are January, February, November and December (UV index 2).
Average cloud cover in September
Portland, OR
- Average cloud cover in September: 33
The month with the most cloud cover is February (Cloud cover 58).
The month with the least cloud cover is August (Cloud cover 23).
Average visibility in September
Portland, OR
- Average visibility in September: 6mi
The months with the highest visibility are July, August and September (6mi).
The months with the lowest visibility are January, February, March, April, May, June, October, November and December (5mi).
