May Weather in Portland, United States

Last updated: June 24, 2025

In Portland, United States, the average temperature in May hovers around 17°C (63°F). Visitors can experience a range from a chilly -1°C (30°F) to a warm 34°C (93°F). This month sees 127 mm (5.0 in) of precipitation spread over 14 days, contributing to an average humidity level of 81%. Whether you enjoy a brisk breeze or a warm day, there's something for everyone in this varied climate!

May Temperature in Portland

In May in Portland, the average temperature is 17°C (63°F). The maximum can reach 34°C (93°F), while the minimum can drop as low as -1°C (30°F). Travelers should be prepared for a wide range of temperatures and pack accordingly.

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 17°C (63°F), with highs reaching up to 34°C (93°F) and lows dropping to around -1°C (30°F).

Data source: Temperature data for Portland generated using information from the Copernicus Climate Change Service.

May Precipitation in Portland

In Portland in May, the total precipitation amount is 127 mm (5.0 in), occurring over the course of 14 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 127 mm (5.0 inches) of precipitation spread over approximately 14 days.

Data source: Precipitation data for May generated using information from the Copernicus Climate Change Service.

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Millimeters (mm) Inches (in)

May Humidity in Portland

In Portland in May humidity is 81%. With an average temperature of 17°C (63°F), this humidity feels like a warm blanket enveloping you, making travel slightly oppressive and calling for frequent breaks in air-conditioned spaces to recharge and enjoy your journey comfortably.

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 81%, offering insight into how humid the weather typically is during this month.

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.

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.
	Temperature	Precipitation	Humidity	UV
January Weather	-2°C (29°F)	74 mm (2.9 inches)	85%	moderate
February Weather	0°C (32°F)	88 mm (3.4 inches)	85%	moderate
March Weather	5°C (42°F)	101 mm (4.0 inches)	86%	high
April Weather	10°C (51°F)	93 mm (3.7 inches)	87%	very high
May Weather	17°C (63°F)	127 mm (5.0 inches)	81%	very high
June Weather	22°C (73°F)	114 mm (4.5 inches)	82%	extreme
July Weather	24°C (76°F)	101 mm (4.0 inches)	81%	very high
August Weather	23°C (74°F)	102 mm (4.0 inches)	79%	very high
September Weather	20°C (69°F)	75 mm (2.9 inches)	78%	very high
October Weather	14°C (57°F)	97 mm (3.8 inches)	81%	high
November Weather	5°C (42°F)	82 mm (3.2 inches)	89%	moderate
December Weather	2°C (35°F)	67 mm (2.7 inches)	86%	low