May Weather in Portland, United States

Last updated: June 24, 2025

In Portland, United States, the average temperature in May hovers around 26°C (79°F), creating a warm and inviting atmosphere. However, be prepared for fluctuations, as temperatures can dip to a minimum of 14°C (57°F) and rise to a maximum of 33°C (92°F). With an average precipitation of 138 mm (5.4 in) spread over 12 days, and a humidity level of 81%, expect a lush, vibrant environment influenced by the moisture in the air.

May Temperature in Portland

In May in Portland, the average temperature is 26°C (79°F). Maximums can reach 33°C (92°F) and minimums can be as low as 14°C (57°F). This makes it an ideal time for travelers to enjoy pleasant weather while exploring the sights.

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 26°C (79°F), with highs reaching up to 33°C (92°F) and lows dropping to around 14°C (57°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 precipitation amount is 138 mm (5.4 in) spread over a period 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 138 mm (5.4 inches) of precipitation spread over approximately 12 days.

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

Choose your preferred precipitation unit

Millimeters (mm) Inches (in)

May Humidity in Portland

In Portland in May, humidity is 81%. With an average temperature of 26°C (79°F), this humidity feels like a warm, heavy blanket wrapping around you, making outdoor adventures stickier and more draining, yet still vibrant with life—perfect for exploring local culture, but you'll want to take frequent breaks and stay hydrated.

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 11, which corresponds to an extreme Exposure Category. With a time to burn of just 10 minutes, it's essential to take precautions. For more details, 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 11, which falls under the extreme 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	14°C (58°F)	39 mm (1.5 inches)	78%	moderate
February Weather	16°C (60°F)	31 mm (1.2 inches)	82%	very high
March Weather	20°C (68°F)	52 mm (2.1 inches)	79%	very high
April Weather	23°C (73°F)	44 mm (1.7 inches)	82%	extreme
May Weather	26°C (79°F)	138 mm (5.4 inches)	81%	extreme
June Weather	28°C (83°F)	136 mm (5.4 inches)	77%	extreme
July Weather	29°C (84°F)	101 mm (4.0 inches)	78%	extreme
August Weather	29°C (85°F)	81 mm (3.2 inches)	78%	extreme
September Weather	28°C (82°F)	141 mm (5.6 inches)	79%	extreme
October Weather	24°C (75°F)	77 mm (3.0 inches)	77%	very high
November Weather	19°C (66°F)	51 mm (2.0 inches)	78%	high
December Weather	16°C (61°F)	47 mm (1.9 inches)	80%	moderate