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May Weather in Portland, United States

Last updated: June 24, 2025

In May, the average temperature in Portland, United States hovers around 15°C (60°F). Expect a range from a chilly -2°C (28°F) at its lowest to a sizzling 35°C (95°F) at its peak. With 136 mm (5.4 in) of precipitation spread over 15 days, be prepared for occasional showers. The average humidity levels are a muggy 82%, adding to the overall atmosphere.

May Temperature in Portland

In May in Portland, the average temperature is 15°C (60°F). The maximum can reach 35°C (95°F), while the minimum can drop as low as -2°C (28°F). Be prepared for a wide range of temperatures while traveling during this time.

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 15°C (60°F), with highs reaching up to 35°C (95°F) and lows dropping to around -2°C (28°F).
JanFebMarAprMayJunJulAugSepOctNovDec262737476070757265533832
Data source: Temperature data for Portland generated using information from the Copernicus Climate Change Service.
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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 136 mm (5.4 in) over a period of 15 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 136 mm (5.4 inches) of precipitation spread over approximately 15 days.
JanFebMarAprMayJunJulAugSepOctNovDec6771688713610682681081276463
Data source: Precipitation data for May generated using information from the Copernicus Climate Change Service.
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May Humidity in Portland

In Portland in May humidity is 82%. With an average temperature of 15°C (60°F), this humidity feels like a heavy blanket wrapping around you, making outdoor activities feel sticky and draining, which can hinder your travel experience.

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%87%86%87%82%81%78%79%80%82%87%86%
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 is 9, which corresponds to a very high Exposure Category. The time to burn is just 15 minutes, so it's essential to take precautions. For 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 9, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec24589101097532
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 Weather-3°C (26°F)67 mm (2.6 inches)87%low
February Weather-3°C (27°F)71 mm (2.8 inches)87%moderate
March Weather3°C (37°F)68 mm (2.7 inches)86%moderate
April Weather8°C (47°F)87 mm (3.4 inches)87%very high
May Weather15°C (60°F)136 mm (5.4 inches)82%very high
June Weather21°C (70°F)106 mm (4.2 inches)81%very high
July Weather24°C (75°F)82 mm (3.2 inches)78%very high
August Weather22°C (72°F)68 mm (2.7 inches)79%very high
September Weather18°C (65°F)108 mm (4.3 inches)79%high
October Weather12°C (53°F)127 mm (5.0 inches)82%moderate
November Weather4°C (39°F)64 mm (2.5 inches)87%moderate
December Weather0°C (32°F)63 mm (2.5 inches)86%low

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