Summer Weather at Seattle-Tacoma International Airport Washington, United StatesDaily high temperatures increase by 7°F, from 68°F to 75°F, rarely falling below 59°F or exceeding 89°F. The highest daily average high temperature is 78°F on August 2. Daily low temperatures increase by 4°F, from 51°F to 56°F, rarely falling below 47°F or exceeding 62°F. The highest daily average low temperature is 58°F on August 2. For reference, on August 2, the hottest day of the year, temperatures at Seattle-Tacoma International Airport typically range from 58°F to 78°F, while on December 22, the coldest day of the year, they range from 37°F to 45°F. The figure below shows you a compact characterization of the hourly average summer temperatures. 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. Paris, France (5,011 miles away) is the far-away foreign place with temperatures most similar to Seattle-Tacoma International Airport (view comparison). CloudsThe summer at Seattle-Tacoma International Airport experiences very rapidly decreasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy decreasing from 54% to 34%. The lowest chance of overcast or mostly cloudy conditions is 25% on August 2. The clearest day of the summer is August 2, with clear, mostly clear, or partly cloudy conditions 75% of the time. For reference, on January 19, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 73%, while on August 2, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 75%. PrecipitationA wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. At Seattle-Tacoma International Airport, the chance of a wet day over the course of the summer is very rapidly decreasing, starting the season at 29% and ending it at 16%. For reference, the year's highest daily chance of a wet day is 57% on November 17, and its lowest chance is 8% on August 10. RainfallTo show variation within the season and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day. The average sliding 31-day rainfall during the summer at Seattle-Tacoma International Airport is decreasing, starting the season at 2.0 inches, when it rarely exceeds 3.4 inches or falls below 0.6 inches, and ending the season at 1.3 inches, when it rarely exceeds 2.9 inches or falls below 0.1 inches. The lowest average 31-day accumulation is 0.6 inches on July 29. SunOver the course of the summer at Seattle-Tacoma International Airport, the length of the day is very rapidly decreasing. From the start to the end of the season, the length of the day decreases by 2 hours, 21 minutes, implying an average daily decrease of 1 minute, 33 seconds, and weekly decrease of 10 minutes, 50 seconds. The shortest day of the summer is August 31, with 13 hours, 22 minutes of daylight and the longest day is June 20, with 15 hours, 58 minutes of daylight. The earliest sunrise of the summer at Seattle-Tacoma International Airport is 5:11 AM on June 15 and the latest sunrise is 1 hour, 16 minutes later at 6:27 AM on August 31. The latest sunset is 9:10 PM on June 24 and the earliest sunset is 1 hour, 20 minutes earlier at 7:50 PM on August 31. Daylight saving time is observed at Seattle-Tacoma International Airport during 2024, but it neither starts nor ends during the summer, so the entire season is in daylight saving time. For reference, on June 20, the longest day of the year, the Sun rises at 5:12 AM and sets 15 hours, 58 minutes later, at 9:09 PM, while on December 21, the shortest day of the year, it rises at 7:54 AM and sets 8 hours, 27 minutes later, at 4:21 PM. The figure below presents a compact representation of the sun's elevation (the angle of the sun above the horizon) and azimuth (its compass bearing) for every hour of every day in the reporting period. The horizontal axis is the day of the year and the vertical axis is the hour of the day. For a given day and hour of that day, the background color indicates the azimuth of the sun at that moment. The black isolines are contours of constant solar elevation. MoonThe figure below presents a compact representation of key lunar data for the summer of 2024. 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. The label associated with each bar indicates the date and time that the phase is obtained, and the companion time labels indicate the rise and set times of the Moon for the nearest time interval in which the moon is above the horizon. HumidityWe 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 at Seattle-Tacoma International Airport is essentially constant during the summer, remaining around 0% throughout. For reference, on August 3, the muggiest day of the year, there are muggy conditions 0% of the time, while on January 1, the least muggy day of the year, there are muggy conditions 0% of the time. WindThis 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 at Seattle-Tacoma International Airport is essentially constant during the summer, remaining within 0.3 miles per hour of 3.3 miles per hour throughout. For reference, on November 30, the windiest day of the year, the daily average wind speed is 5.4 miles per hour, while on August 1, the calmest day of the year, the daily average wind speed is 3.0 miles per hour. The lowest daily average wind speed during the summer is 3.0 miles per hour on August 1. The wind direction at Seattle-Tacoma International Airport during the summer is predominantly out of the south from June 1 to July 7 and the north from July 7 to August 31. Water TemperatureSeattle-Tacoma International Airport 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 at Seattle-Tacoma International Airport is gradually increasing during the summer, rising by 4°F, from 53°F to 57°F, over the course of the season. The highest average surface water temperature during the summer is 57°F on August 21. Growing SeasonDefinitions 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 at Seattle-Tacoma International Airport typically lasts for 9.1 months (279 days), from around February 22 to around November 27, rarely starting before January 23 or after March 16, and rarely ending before November 3 or after December 20. The summer at Seattle-Tacoma International Airport is reliably fully within the growing season. 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. The average accumulated growing degree days at Seattle-Tacoma International Airport are very rapidly increasing during the summer, increasing by 1,252°F, from 346°F to 1,598°F, over the course of the season. Solar EnergyThis 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 at Seattle-Tacoma International Airport is gradually decreasing during the summer, falling by 0.7 kWh, from 5.9 kWh to 5.2 kWh, over the course of the season. The highest average daily incident shortwave solar energy during the summer is 6.8 kWh on July 20. TopographyFor the purposes of this report, the geographical coordinates of Seattle-Tacoma International Airport are 47.449 deg latitude, -122.309 deg longitude, and 397 ft elevation. The topography within 2 miles of Seattle-Tacoma International Airport contains only modest variations in elevation, with a maximum elevation change of 469 feet and an average elevation above sea level of 341 feet. Within 10 miles contains only modest variations in elevation (1,109 feet). Within 50 miles contains very significant variations in elevation (14,360 feet). The area within 2 miles of Seattle-Tacoma International Airport is covered by artificial surfaces (99%), within 10 miles by artificial surfaces (55%) and water (28%), and within 50 miles by trees (53%) and artificial surfaces (14%). Data SourcesThis report illustrates the typical weather at Seattle-Tacoma International Airport, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016. Temperature and Dew PointSeattle-Tacoma International Airport has a weather station that reported reliably enough during the analysis period that we have included it in our network. When available, historical temperature and dew point measurements are taken directly from this weather station. These records are obtained from NOAA's Integrated Surface Hourly data set, falling back on ICAO METAR records as required. In the case of missing or erroneous measurements from this station, we fall back on records from nearby stations, adjusted according to typical seasonal and diurnal intra-station differences. For a given day of the year and hour of the day, the fallback station is selected to minimize the prediction error over the years for which there are measurements for both stations. The stations on which we may fall back include but are not limited to King County International Airport, Renton Municipal Airport, Tacoma Narrows Airport, McChord Field Airport (Joint Base Lewis-McChord), Pierce County Airport Thun Field, Madigan Hospital Heliport, Bremerton National Airport, and Snohomish County Airport (Paine Field). Other DataAll 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 © OpenStreetMap contributors. DisclaimerThe 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. Please review our full terms contained on our Terms of Service page. |