Average Weather in Portland Oregon, United States
In Portland, the summers are short, warm, dry, and mostly clear and the winters are chilly, wet, and overcast. Over the course of the year, the temperature typically varies from 36°F to 84°F and is rarely below 26°F or above 95°F.
The warm season lasts for 2.9 months, from June 23 to September 19, with an average daily high temperature above 76°F. The hottest day of the year is August 3, with an average high of 84°F and low of 58°F.
The cool season lasts for 3.3 months, from November 14 to February 22, with an average daily high temperature below 53°F. The coldest day of the year is December 30, with an average low of 36°F and high of 45°F.
Average High and Low Temperature
The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, 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 Portland, the average percentage of the sky covered by clouds experiences extreme seasonal variation over the course of the year.
The clearer part of the year in Portland begins around June 11 and lasts for 3.9 months, ending around October 8. On August 3, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 82% of the time, and overcast or mostly cloudy 18% of the time.
The cloudier part of the year begins around October 8 and lasts for 8.1 months, ending around June 11. On January 16, the cloudiest day of the year, the sky is overcast or mostly cloudy 76% of the time, and clear, mostly clear, or partly cloudy 24% of the time.
Cloud Cover Categories
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Portland varies very significantly throughout the year.
The wetter season lasts 6.8 months, from October 13 to May 8, with a greater than 32% chance of a given day being a wet day. The chance of a wet day peaks at 59% on November 27.
The drier season lasts 5.2 months, from May 8 to October 13. The smallest chance of a wet day is 4% on August 3.
Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 58% on November 18.
Daily Chance of Precipitation
To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. Portland experiences extreme seasonal variation in monthly rainfall.
The rainy period of the year lasts for 11 months, from August 14 to July 16, with a sliding 31-day rainfall of at least 0.5 inches. The most rain falls during the 31 days centered around November 29, with an average total accumulation of 9.4 inches.
The rainless period of the year lasts for 4.1 weeks, from July 16 to August 14. The least rain falls around July 29, with an average total accumulation of 0.4 inches.
Average Monthly Rainfall
We report snowfall in liquid-equivalent terms. The actual depth of new snowfall is typically between 5 and 10 times the liquid-equivalent amount, assuming the ground is frozen. Colder, drier snow tends to be on the higher end of that range and warmer, wetter snow on the lower end.
As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Portland experiences some seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 2.5 months, from December 1 to February 16, with a sliding 31-day liquid-equivalent snowfall of at least 0.1 inches. The most snow falls during the 31 days centered around January 6, with an average total liquid-equivalent accumulation of 0.3 inches.
The snowless period of the year lasts for 9.5 months, from February 16 to December 1. The least snow falls around July 19, with an average total liquid-equivalent accumulation of 0.0 inches.
Average Liquid-Equivalent Monthly Snowfall
The length of the day in Portland varies significantly over the course of the year. In 2017, the shortest day is December 21, with 8 hours, 42 minutes of daylight; the longest day is June 20, with 15 hours, 41 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 5:21 AM on June 15, and the latest sunrise is 2 hours, 34 minutes later at 7:55 AM on November 4. The earliest sunset is at 4:27 PM on December 10, and the latest sunset is 4 hours, 37 minutes later at 9:03 PM on June 26.
Daylight saving time (DST) is observed in Portland during 2017, starting in the spring on March 12, lasting 7.8 months, and ending in the fall on November 5.
Sunrise & Sunset with Twilight and Daylight Saving Time
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 perceived humidity level in Portland, as measured by the percentage of time in which the humidity comfort level is muggy, oppressive, or miserable, does not vary significantly over the course of the year, remaining a virtually constant 0% throughout.
Humidity Comfort Levels
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 experiences mild seasonal variation over the course of the year.
The windier part of the year lasts for 4.7 months, from October 28 to March 19, with average wind speeds of more than 2.8 miles per hour. The windiest day of the year is December 3, with an average hourly wind speed of 3.4 miles per hour.
The calmer time of year lasts for 7.3 months, from March 19 to October 28. The calmest day of the year is August 23, with an average hourly wind speed of 2.3 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in Portland varies throughout the year.
The wind is most often from the south for 1.1 weeks, from January 12 to January 20; for 2.1 months, from February 4 to April 8; and for 2.7 months, from October 4 to December 27, with a peak percentage of 49% on November 18. The wind is most often from the east for 2.1 weeks, from January 20 to February 4 and for 2.3 weeks, from December 27 to January 12, with a peak percentage of 44% on January 27. The wind is most often from the west for 5.9 months, from April 8 to October 4, with a peak percentage of 58% on August 7.
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 water temperature experiences some seasonal variation over the course of the year.
The time of year with warmer water lasts for 3.4 months, from June 15 to September 26, with an average temperature above 57°F. The day of the year with the warmest water is August 22, with an average temperature of 59°F.
The time of year with cooler water lasts for 4.3 months, from December 8 to April 16, with an average temperature below 51°F. The day of the year with the coolest water is February 14, with an average temperature of 49°F.
Average Water Temperature
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 experiences extreme seasonal variation over the course of the year.
The brighter period of the year lasts for 2.8 months, from May 30 to August 25, with an average daily incident shortwave energy per square meter above 6.0 kWh. The brightest day of the year is July 16, with an average of 7.3 kWh.
The darker period of the year lasts for 3.9 months, from October 25 to February 22, with an average daily incident shortwave energy per square meter below 2.3 kWh. The darkest day of the year is December 26, with an average of 1.0 kWh.
Average Daily Incident Shortwave Solar Energy
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, 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.