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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 16°C (61°F), presenting a delightful mix of mildness. However, be prepared for temperature fluctuations ranging from a brisk -1°C (31°F) to a warm 32°C (90°F). As you navigate this season, expect 135 mm (5.3 in) of precipitation over approximately 12 days, while the average humidity settles at 75%, adding to the atmosphere.

May Temperature in Portland

In May in Portland the average temperature is 16°C (61°F). Maximums can reach 32°C (90°F), while minimums can drop as low as -1°C (31°F). This wide temperature range means that travelers should be prepared for both warm days and chilly evenings.

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 16°C (61°F), with highs reaching up to 32°C (90°F) and lows dropping to around -1°C (31°F).
JanFebMarAprMayJunJulAugSepOctNovDec313439506069757367574235
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 135 mm (5.3 in), occurring over the course of 12 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 135 mm (5.3 inches) of precipitation spread over approximately 12 days.
JanFebMarAprMayJunJulAugSepOctNovDec71102941101369212412510714190106
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 75%. With an average temperature of 16°C (61°F), this humidity feels like a warm, muggy embrace, making traveling somewhat uncomfortable as you may find yourself constantly adjusting your clothing and seeking shade to escape the sticky air.

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 75%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec87%85%85%83%75%74%65%62%66%79%87%85%
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.
JanFebMarAprMayJunJulAugSepOctNovDec356910101098642
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-1°C (31°F)71 mm (2.8 inches)87%moderate
February Weather1°C (34°F)102 mm (4.0 inches)85%moderate
March Weather4°C (39°F)94 mm (3.7 inches)85%high
April Weather10°C (50°F)110 mm (4.3 inches)83%very high
May Weather16°C (61°F)135 mm (5.3 inches)75%very high
June Weather21°C (69°F)92 mm (3.6 inches)73%very high
July Weather24°C (75°F)124 mm (4.9 inches)65%very high
August Weather23°C (73°F)125 mm (4.9 inches)62%very high
September Weather19°C (67°F)107 mm (4.2 inches)66%very high
October Weather14°C (57°F)141 mm (5.5 inches)79%high
November Weather6°C (42°F)90 mm (3.5 inches)87%moderate
December Weather2°C (35°F)106 mm (4.2 inches)85%low

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