May Weather in Portland, United States

Last updated: June 24, 2025

In Portland, United States, the average temperature in May hovers around 21°C (70°F). During this time, expect a minimum of 4°C (39°F) and soaring to a maximum of 33°C (92°F). With an average humidity of 82%, you might feel the warmth even more. Be prepared for some rain, as 122 mm (4.8 in) of precipitation typically falls over 13 days.

May Temperature in Portland

In May in Portland, the average temperature is 21°C (70°F). The maximum can reach 33°C (92°F), while the minimum can dip as low as 4°C (39°F). This weather makes Portland an ideal destination for travelers seeking mild temperatures and a range of outdoor activities.

May Weather in Portland: Daily Temperature Highs, Lows, and Averages

The chart illustrates May temperature patterns in Portland, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Portland, May typically has an average temperature of 21°C (70°F), with highs reaching up to 33°C (92°F) and lows dropping to around 4°C (39°F).
JanFebMarAprMayJunJulAugSepOctNovDec404452597076807873634845
Data source: Temperature data for Portland generated using information from the Copernicus Climate Change Service.
Choose your preferred temperature unit
The average of daily temperatures (24 hours) calculated across all days in the month.

May Precipitation in Portland

In Portland in May, the precipitation amount is 122 mm (4.8 in) recorded over a span of 13 days.

May Precipitation Trends in Portland

The chart displays monthly precipitation patterns in Portland, with values for each month alongside May’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how May’s conditions compare to those of other months. In Portland, May typically receives around 122 mm (4.8 inches) of precipitation spread over approximately 13 days.
JanFebMarAprMayJunJulAugSepOctNovDec10518515715012214112512412513888147
Data source: Precipitation data for May generated using information from the Copernicus Climate Change Service.
Choose your preferred precipitation unit

May Humidity in Portland

In Portland in May, humidity is 82%. With an average temperature of 21°C (70°F), this humidity feels like a warm, sticky embrace that can quickly lead to discomfort for travelers, making outdoor activities less enjoyable and requiring frequent breaks for hydration.

May Average Humidity in Portland

This chart illustrates the average monthly humidity levels in Portland, with May’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In May, average humidity in Portland is approximately 82%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec87%86%86%82%83%83%80%74%71%78%88%88%
Data source: Humidity data for May generated using information from the Copernicus Climate Change Service.

May UV Index in Portland

In Portland in May, the maximum UV index reaches 10, which corresponds to a very high Exposure Category. With a time to burn of just 15 minutes, it's crucial to take precautions. For more detailed information, you can check the Hourly UV Index in Portland.

Maximum UV Index Levels in Portland for May

The chart shows the monthly maximum UV Index (UVI) for Portland in May, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In May, the maximum UV index in Portland typically reaches 10, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec36710101111109753
Data source: Portland May UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

How May Weather in Portland Compares to Other Months

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.

This table compares monthly weather conditions in Portland, showing how May’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather4°C (40°F)105 mm (4.1 inches)87%moderate
February Weather7°C (44°F)185 mm (7.3 inches)86%high
March Weather11°C (52°F)157 mm (6.2 inches)86%high
April Weather15°C (59°F)150 mm (5.9 inches)82%very high
May Weather21°C (70°F)122 mm (4.8 inches)82%very high
June Weather25°C (77°F)141 mm (5.5 inches)83%extreme
July Weather27°C (80°F)125 mm (4.9 inches)80%extreme
August Weather25°C (78°F)124 mm (4.9 inches)74%very high
September Weather23°C (74°F)125 mm (4.9 inches)71%very high
October Weather17°C (63°F)138 mm (5.4 inches)78%high
November Weather9°C (48°F)88 mm (3.4 inches)88%moderate
December Weather7°C (45°F)147 mm (5.8 inches)88%moderate

Compare Portland's Climate with Cities Worldwide