Portland Weather in May

May brings warm weather to Portland, Oregon and carries on the springtime trend of declining cloud and rain.

This page gives detailed information on the typical May temperature, precipitation, sun, humidity, wind and storms for Portland. 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

69 °F May average high 21 °C
48 °F May average low 9 °C
13 days 70 °F max. or more (12 °C)
20 days 50 °F min. or less (10 °C)

Most days in May warm to over 60 degrees Fahrenheit (16 degrees Celsius) in Portland. The city averages five days this month when the thermometer reaches into the 80s °F (over 26 °C). Temperatures above 90 °F (32 °C) sometimes occur briefly this time of year.

The thermometer dips to 40 °F (4 °C) or below on an average of 2 nights this month. But May does not normally get cold enough for frost.

Rainy Weather iconRain

2.8 in total precipitation 70 mm
14 days of rain

Half the time, Portland receives 1.7 to 4.0 inches (42 to 102 mm) of rainfall in May. One in four years has drier weather, while another one in four is wetter.

Sunny Weather iconSun

57 % sunshine
5 days clear skies

The sun's rays reach the ground in Portland during 57 percent of daylight hours on average in May, for a total of 264 hours in the month. Typically on 5 days this month the sky is mainly clear, with at most 30 percent cloud cover.

Sunlight in May at Portland lasts for 14 hours and 55 minutes a day on average. The shortest day of the month is the 1st with 14 hours and 20 minutes of daylight. By the end of the month, the days have lengthened to 15:26 from sunrise to sunset. These durations can vary by a minute or two from year to year.

Humid Weather iconHumidity

69 % May average humidity

The relative humidity in Portland during May usually peaks at 84 percent in the morning then drops to 52 percent by mid afternoon.

Local Time1 am4 am7 am10 am1 pm4 pm7 pm10 pm
Humidity % 80 84 80 66 56 52 60 72

Windy Weather iconWind

7.1 mph May wind speed average 11.4 kph

May is less windy than most other months in Portland.

Stormy Weather iconStorms

2 days rainfall of 0.5 inches (13 mm) or more
1 day with thunderstorms in May

A storm that soaks Portland in an inch (25 mm) or more of rain in one day during May happens about once a decade. Portland usually sees more thunderstorms in May than any other month.


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.

Portland Weather
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