Last updated: June 24, 2025
In May, the average temperature in Portland, United States hovers around 13°C (56°F). Expect a minimum temperature that can drop to -5°C (24°F), while peaks can reach up to 34°C (94°F). Be prepared for some rain, with an average precipitation of 55 mm (2.2 in) over 9 days. Additionally, with an average humidity of 75%, it's a good idea to pack accordingly!
In May in Portland, the average temperature is 13°C (56°F), with maximums reaching 34°C (94°F) and minimums dropping as low as -5°C (24°F). This variation in temperatures makes Portland an ideal destination for travelers seeking both warm days and cooler evenings.
In Portland in May, the precipitation amount is 55 mm (2.2 in) over a span of 9 days.
In Portland in May humidity is 75%. With an average temperature of 13°C (56°F), this humidity feels like a damp chill enveloping you, making travel a bit uncomfortable, as the moisture in the air clings to your skin and can dampen your spirits as well as your clothes.
In Portland in May, the maximum UV index is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to the Hourly UV Index in Portland.
UV Risk Categories
Weather in Portland varies notably across the year, with each month offering distinct climate conditions. This page compares May’s weather to other months in Portland, focusing on differences in temperature, rainfall, humidity, and UV levels.
| 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 |