Average Weather in May in Portland Oregon, United States
In Portland, the month of May is characterized by rising daily high temperatures, with daily highs increasing by 6°F, from 65°F to 71°F over the course of the month, and rarely exceeding 84°F or dropping below 55°F.
Daily low temperatures increase by 5°F, from 46°F to 51°F, rarely falling below 40°F or exceeding 57°F.
For reference, on August 3, the hottest day of the year, temperatures in Portland typically range from 58°F to 84°F, while on December 30, the coldest day of the year, they range from 36°F to 45°F.
Average High and Low Temperature in May
The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on May. The horizontal axis is the day, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.
Average Hourly Temperature in May
The month of May in Portland experiences gradually decreasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy decreasing from 59% to 53%.
The clearest day of the month is May 31, with clear, mostly clear, or partly cloudy conditions 47% of the time.
For reference, on January 16, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 76%, while on August 3, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 82%.
Cloud Cover in May
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Portland, the chance of a wet day over the course of May is gradually decreasing, starting the month at 33% and ending it at 29%.
For reference, the year's highest daily chance of a wet day is 59% on November 27, and its lowest chance is 4% on August 3.
Probability of Precipitation in May
To show variation within the month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day.
The average sliding 31-day rainfall during May in Portland is decreasing, starting the month at 3.0 inches, when it rarely exceeds 5.0 inches or falls below 1.2 inches, and ending the month at 2.2 inches, when it rarely exceeds 3.9 inches or falls below 0.6 inches.
Average Monthly Rainfall in May
Over the course of May in Portland, the length of the day is rapidly increasing. From the start to the end of the month, the length of the day increases by 1 hour, 6 minutes, implying an average daily increase of 2 minutes, 12 seconds, and weekly increase of 15 minutes, 27 seconds.
The shortest day of the month is May 1, with 14 hours, 20 minutes of daylight and the longest day is May 31, with 15 hours, 26 minutes of daylight.
Hours of Daylight and Twilight in May
The latest sunrise of the month in Portland is 5:58 AM on May 1 and the earliest sunrise is 33 minutes earlier at 5:25 AM on May 31.
The earliest sunset is 8:18 PM on May 1 and the latest sunset is 34 minutes later at 8:51 PM on May 31.
Daylight saving time is observed in Portland during 2017, but it neither starts nor ends during May, so the entire month is in daylight saving time.
For reference, on June 21, the longest day of the year, the Sun rises at 5:21 AM and sets 15 hours, 41 minutes later, at 9:03 PM, while on December 21, the shortest day of the year, it rises at 7:48 AM and sets 8 hours, 42 minutes later, at 4:30 PM.
Sunrise & Sunset with Twilight in May
We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.
The chance that a given day will be muggy in Portland is essentially constant during May, remaining around 0% throughout.
For reference, on August 5, the muggiest day of the year, there are muggy conditions 1% of the time, while on January 1, the leasy muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in May
This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.
The average hourly wind speed in Portland is essentially constant during May, remaining within 0.1 miles per hour of 2.4 miles per hour throughout.
For reference, on December 3, the windiest day of the year, the daily average wind speed is 3.4 miles per hour, while on August 23, the calmest day of the year, the daily average wind speed is 2.3 miles per hour.
Average Wind Speed in May
Wind Direction in May
Portland is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.
The average surface water temperature in Portland is gradually increasing during May, rising by 3°F, from 52°F to 55°F, over the course of the month.
Average Water Temperature in May
This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.
The average daily incident shortwave solar energy in Portland is gradually increasing during May, rising by 0.8 kWh, from 5.2 kWh to 6.1 kWh, over the course of the month.
Average Daily Incident Shortwave Solar Energy in May
For the purposes of this report, the geographical coordinates of Portland are 45.523 deg latitude, -122.676 deg longitude, and 161 ft elevation.
The topography within 2 miles of Portland contains very significant variations in elevation, with a maximum elevation change of 866 feet and an average elevation above sea level of 161 feet. Within 10 miles also contains very significant variations in elevation (1,253 feet). Within 50 miles contains very significant variations in elevation (11,161 feet).
The area within 2 miles of Portland is covered by artificial surfaces (65%), water (19%), and trees (14%), within 10 miles by artificial surfaces (68%) and trees (12%), and within 50 miles by trees (47%) and shrubs (20%).
This report illustrates the typical weather in Portland year round, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.
Temperature and Dew Point
There are 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Portland.
For each station, the records are corrected for the elevation difference between that station and Portland according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.
The estimated value at Portland is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Portland and a given station.
The stations contributing to this reconstruction are: Portland International Airport (65%, 10 kilometers, northeast); Portland-Hillsboro Airport (23%, 21 kilometers, west); and Aurora State Airport (13%, 31 kilometers, south).
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , by Jean Meeus.
All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.
Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.
Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.
Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .
Time zones for aiports and weather stations are provided by AskGeo.com .
Maps are © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.