Climate and Average Weather Year Round in Seattle Washington, United States
In Seattle, the summers are short, warm, dry, and partly cloudy and the winters are very cold, wet, and mostly cloudy. Over the course of the year, the temperature typically varies from 37°F to 79°F and is rarely below 28°F or above 88°F.
Based on the tourism score, the best time of year to visit Seattle for warm-weather activities is from early July to late August.
Climate in Seattle
The warm season lasts for 2.8 months, from June 21 to September 13, with an average daily high temperature above 72°F. The hottest month of the year in Seattle is August, with an average high of 77°F and low of 58°F.
The cool season lasts for 3.6 months, from November 12 to March 1, with an average daily high temperature below 53°F. The coldest month of the year in Seattle is December, with an average low of 38°F and high of 47°F.
Average High and Low Temperature in Seattle
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 Seattle
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
In Seattle, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.
The clearer part of the year in Seattle begins around June 13 and lasts for 3.8 months, ending around October 8.
The clearest month of the year in Seattle is August, during which on average the sky is clear, mostly clear, or partly cloudy 70% of the time.
The cloudier part of the year begins around October 8 and lasts for 8.2 months, ending around June 13.
The cloudiest month of the year in Seattle is January, during which on average the sky is overcast or mostly cloudy 71% of the time.
Cloud Cover Categories in Seattle
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Seattle varies significantly throughout the year.
The wetter season lasts 6.6 months, from October 10 to April 30, with a greater than 33% chance of a given day being a wet day. The month with the most wet days in Seattle is November, with an average of 16.7 days with at least 0.04 inches of precipitation.
The drier season lasts 5.4 months, from April 30 to October 10. The month with the fewest wet days in Seattle is August, with an average of 3.5 days with at least 0.04 inches of precipitation.
Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. The month with the most days of rain alone in Seattle is November, with an average of 16.5 days. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 56% on November 18.
Daily Chance of Precipitation in Seattle
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. Seattle experiences extreme seasonal variation in monthly rainfall.
Rain falls throughout the year in Seattle. The month with the most rain in Seattle is November, with an average rainfall of 7.5 inches.
The month with the least rain in Seattle is July, with an average rainfall of 0.7 inches.
Average Monthly Rainfall in Seattle
As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Seattle experiences some seasonal variation in monthly snowfall.
The snowy period of the year lasts for 1.3 months, from December 12 to January 20, with a sliding 31-day snowfall of at least 1.0 inches. The month with the most snow in Seattle is January, with an average snowfall of 1.2 inches.
The snowless period of the year lasts for 11 months, from January 20 to December 12. The least snow falls around July 1, with an average total accumulation of 0.0 inches.
Average Monthly Snowfall in Seattle
The length of the day in Seattle varies significantly over the course of the year. In 2022, the shortest day is December 21, with 8 hours, 26 minutes of daylight; the longest day is June 21, with 15 hours, 59 minutes of daylight.
Hours of Daylight and Twilight in Seattle
The earliest sunrise is at 5:10 AM on June 16, and the latest sunrise is 2 hours, 49 minutes later at 7:59 AM on November 5. The earliest sunset is at 4:17 PM on December 11, and the latest sunset is 4 hours, 54 minutes later at 9:11 PM on June 25.
Daylight saving time (DST) is observed in Seattle during 2022, starting in the spring on March 13, lasting 7.8 months, and ending in the fall on November 6.
Sunrise & Sunset with Twilight and Daylight Saving Time in Seattle
The figure below presents a compact representation of key lunar data for 2022. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases.
Moon Rise, Set & Phases in Seattle
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 Seattle, 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 in Seattle
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
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 Seattle experiences mild seasonal variation over the course of the year.
The windier part of the year lasts for 6.3 months, from October 15 to April 24, with average wind speeds of more than 4.1 miles per hour. The windiest month of the year in Seattle is December, with an average hourly wind speed of 5.1 miles per hour.
The calmer time of year lasts for 5.7 months, from April 24 to October 15. The calmest month of the year in Seattle is July, with an average hourly wind speed of 2.9 miles per hour.
Average Wind Speed in Seattle
The predominant average hourly wind direction in Seattle varies throughout the year.
The wind is most often from the north for 2.6 months, from July 3 to September 20, with a peak percentage of 46% on July 30. The wind is most often from the south for 9.5 months, from September 20 to July 3, with a peak percentage of 57% on January 1.
Wind Direction in Seattle
Seattle 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 3.1 months, from June 24 to September 28, with an average temperature above 54°F. The month of the year in Seattle with the warmest water is August, with an average temperature of 56°F.
The time of year with cooler water lasts for 4.0 months, from December 10 to April 11, with an average temperature below 48°F. The month of the year in Seattle with the coolest water is February, with an average temperature of 46°F.
Average Water Temperature in Seattle
To characterize how pleasant the weather is in Seattle throughout the year, we compute two travel scores.
The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit Seattle for general outdoor tourist activities is from early July to late August, with a peak score in the first week of August.
Tourism Score in Seattle
The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit Seattle for hot-weather activities is from mid July to mid August, with a peak score in the first week of August.
Beach/Pool Score in Seattle
For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.
Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.
Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.
Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.
Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.
Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).
The growing season in Seattle typically lasts for 9.0 months (272 days), from around February 24 to around November 23, rarely starting before January 17 or after March 19, and rarely ending before November 1 or after December 17.
Time Spent in Various Temperature Bands and the Growing Season in Seattle
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.
Based on growing degree days alone, the first spring blooms in Seattle should appear around April 8, only rarely appearing before March 16 or after April 28.
Growing Degree Days in Seattle
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 3.3 months, from May 14 to August 23, with an average daily incident shortwave energy per square meter above 5.6 kWh. The brightest month of the year in Seattle is July, with an average of 6.6 kWh.
The darker period of the year lasts for 3.8 months, from October 26 to February 18, with an average daily incident shortwave energy per square meter below 2.1 kWh. The darkest month of the year in Seattle is December, with an average of 0.9 kWh.
Average Daily Incident Shortwave Solar Energy in Seattle
For the purposes of this report, the geographical coordinates of Seattle are 47.606 deg latitude, -122.332 deg longitude, and 174 ft elevation.
The topography within 2 miles of Seattle contains only modest variations in elevation, with a maximum elevation change of 449 feet and an average elevation above sea level of 135 feet. Within 10 miles contains only modest variations in elevation (1,171 feet). Within 50 miles contains very significant variations in elevation (7,720 feet).
The area within 2 miles of Seattle is covered by artificial surfaces (69%) and water (31%), within 10 miles by artificial surfaces (47%) and water (40%), and within 50 miles by trees (52%) and water (14%).
This report illustrates the typical weather in Seattle, 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 Seattle.
For each station, the records are corrected for the elevation difference between that station and Seattle 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 Seattle is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Seattle and a given station.
The stations contributing to this reconstruction are:
To get a sense of how much these sources agree with each other, you can view a comparison of Seattle and the stations that contribute to our estimates of its temperature history and climate. Please note that each source's contribution is adjusted for elevation and the relative change present in the MERRA-2 data.
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Algorithms 2nd Edition , 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 airports 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.
The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.
We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.
We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader.
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