May Weather in Portland, United States

Last updated: June 24, 2025

In May, the average temperature in Portland, United States hovers around 15°C (59°F). Visitors can expect a range from a chilly -1°C (31°F) to a warm 34°C (93°F). With an average humidity of 75%, the air feels quite moist. Be prepared for 139 mm (5.5 in) of precipitation over 15 days, making it essential to pack an umbrella along with your summer gear!

May Temperature in Portland

In May in Portland, the average temperature is 15°C (59°F), with maximums reaching up to 34°C (93°F) and minimums dropping as low as -1°C (31°F). This suggests that travelers should be prepared for a wide range of weather conditions during their visit.

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 (59°F), with highs reaching up to 34°C (93°F) and lows dropping to around -1°C (31°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 139 mm (5.5 in), occurring over 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 139 mm (5.5 inches) of precipitation spread over approximately 15 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 75%. With an average temperature of 15°C (59°F), this humidity feels like a warm blanket enveloping you, making it feel more oppressive than refreshing, which can be a challenge for travelers seeking comfort while exploring the area.

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.

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.

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	-7°C (20°F)	38 mm (1.5 inches)	84%	low
February Weather	-6°C (21°F)	54 mm (2.1 inches)	85%	moderate
March Weather	2°C (35°F)	60 mm (2.3 inches)	84%	moderate
April Weather	7°C (45°F)	92 mm (3.6 inches)	83%	very high
May Weather	15°C (59°F)	139 mm (5.5 inches)	75%	very high
June Weather	21°C (70°F)	124 mm (4.9 inches)	79%	very high
July Weather	23°C (74°F)	112 mm (4.4 inches)	75%	very high
August Weather	21°C (70°F)	112 mm (4.4 inches)	69%	very high
September Weather	18°C (64°F)	111 mm (4.4 inches)	74%	very high
October Weather	10°C (50°F)	119 mm (4.7 inches)	79%	moderate
November Weather	1°C (35°F)	53 mm (2.1 inches)	88%	moderate
December Weather	-3°C (27°F)	44 mm (1.7 inches)	82%	low