Average Weather on January 20 in Seattle Washington, United States
On January 20, the temperature in Seattle typically ranges from 40°F to 47°F and is rarely below 30°F or above 54°F.
For reference, on August 1, the hottest day of the year, temperatures in Seattle typically range from 59°F to 79°F, while on December 23, the coldest day of the year, they range from 37°F to 46°F.
The coolest time of the day is from 11:30 PM to 9:15 AM, with the coldest at 6:30 AM, at which time the temperature is below 45°F three days out of four, and below 48°F nine days out of ten.
The warmest time of the day is from 12:15 PM to 4:45 PM, with the hottest at 2:45 PM, at which time the temperature is above 43°F three days out of four, and above 39°F nine days out of ten.
The day has gained half its heat by 10:45 AM and lost it again by 7:30 PM.
Average Temperature on January 20
The figure below shows you a compact characterization of the range of temperatures experienced on January 20 throughout the historical record. The horizontal axis is the time of day and the colored stacked areas indicate the percentage of hours spent in various temperature bands.
Temperature Bands on January 20
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
Compared to January 20 (excluding 30 days before and after), December 3 has the most similar daily average high and low temperatures.
The average percentage of the sky covered by clouds in Seattle on January 20 varies over the course of the day.
The cloudiest time of day is around 5:30 AM, at which time the chance of overcast or mostly cloudy conditions is 75%.
The clearest time of day is around 12:30 PM, at which time the chance of clear, mostly clear, or partly cloudy conditions is 31%.
For reference, on January 19, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 72%, while on August 3, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 75%.
Cloud Cover Categories on January 20
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
On average, there is a 49% chance that more than 0.04 inches of total precipitation will fall in Seattle throughout the day on January 20, of which 96% is expected to be rain alone, 1% to be snow alone, and 3% to be a mixture of snow and rain.
For reference, the year's highest daily chance of precipitation is 57% on November 18, and its lowest chance is 8% on August 11.
For those 49% of years with precipitation on January 20, the chart below shows when throughout the day that precipitation is more or less likely to occur, excluding hourly accumulations of less than 0.01 inches. If precipitation were equally likely throughout the day, all hours would report 4.2% (100% divided by 24 hours).
Precipitation is most likely between 1 PM and 2 PM, and least likely between 8 PM and 9 PM.
Hourly Share of Precipitation on January 20
In Seattle on Wednesday, January 20, 2021, the Sun rises at 7:48 AM and sets 9 hours, 4 minutes later, at 4:52 PM. Solar noon is at 12:20 PM.
For reference, on June 21, the longest day of the year, the Sun rises at 5:11 AM and sets 15 hours, 59 minutes later, at 9:10 PM, while on December 21, the shortest day of the year, it rises at 7:54 AM and sets 8 hours, 26 minutes later, at 4:20 PM.
Civil twilight, the period before the Sun has risen or after the Sun has set during which time it is possible to engage in most outdoor activities without artificial lighting, begins and ends 34 minutes before sunrise and after sunset, at 7:14 AM and 5:27 PM respectively.
Nautical twilight, during which time it is possible to clearly discern the horizon (e.g., for navigational purposes), begins and ends 1 hour, 12 minutes before sunrise and after sunset, at 6:36 AM and 6:04 PM respectively.
Astronomical twilight, outside of which it is possible to make the most sensitive of astronomical observations, begins and ends 1 hour, 49 minutes before sunrise and after sunset, at 5:59 AM and 6:41 PM respectively.
Solar Elevation on January 20, 2021
In Seattle on Wednesday, January 20, 2021, the Moon sets at 12:12 AM and rises at 11:31 AM. The phase of the moon is first quarter (at 1:02 PM), with 49% of the disk illuminated.
Lunar Elevation on January 20, 2021
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.
Muggy conditions are essentially unheard-of in Seattle on January 20.
Humidity Comfort Levels on January 20
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 on January 20 remains essentially constant throughout the day, remaining within 0.3 miles per hour of 5.0 miles per hour throughout.
For reference, on November 30, the windiest day of the year, the daily average wind speed is 5.3 miles per hour, while on August 2, the calmest day of the year, the daily average wind speed is 2.8 miles per hour.
Wind Speed on January 20
Over the entire course of January 20 in Seattle, the hourly average wind direction, in order of prevalence, is from the south (59%), east (28%), north (7%), and west (5%).
Wind Direction on January 20
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 surface water temperature does not change appreciably over the course of the day, so this section does not include a chart.
The average surface water temperature on January 20 in Seattle is 47°F, mostly staying between 45°F and 48°F, and rarely falling below 45°F or exceeding 49°F.
For reference, the year's highest average is 56°F on August 20, and its lowest average is 46°F on February 12.
Shortwave Solar Power
This section discusses the incident shortwave solar power 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 peak incident shortwave solar power per square meter is 0.23 kilowatts at around 12:15 PM.
In contrast, the corresponding value on July 21, the brightest day of the year, is 0.77 kilowatts at around 12:00 PM. The corresponding value on December 26, the darkest day of the year, is 0.18 kilowatts at around 11:15 AM.
Shortwave Solar Power on January 20
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: King County International Airport (78%, 9 kilometers, south); Snohomish County Airport (Paine Field) (11%, 34 kilometers, north); and Bremerton National Airport (11%, 35 kilometers, southwest).
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.