Average Weather in December in West Lake Sammamish Washington, United States
Daily high temperatures decrease by 2°F, from 47°F to 45°F, rarely falling below 37°F or exceeding 53°F. The lowest daily average high temperature is 45°F on December 22.
Daily low temperatures are around 37°F, rarely falling below 26°F or exceeding 46°F. The lowest daily average low temperature is 36°F on December 22.
For reference, on August 2, the hottest day of the year, temperatures in West Lake Sammamish typically range from 59°F to 78°F, while on December 22, the coldest day of the year, they range from 36°F to 45°F.
Average High and Low Temperature in December
The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on December. 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 December
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
The month of December in West Lake Sammamish experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 75% throughout the month.
The clearest day of the month is December 31, with clear, mostly clear, or partly cloudy conditions 26% of the time.
For reference, on November 28, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 75%, while on August 2, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 74%.
Cloud Cover Categories in December
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. In West Lake Sammamish, the chance of a wet day over the course of December is decreasing, starting the month at 58% and ending it at 52%.
For reference, the year's highest daily chance of a wet day is 60% on November 17, and its lowest chance is 9% on August 4.
Over the course of December in West Lake Sammamish, the chance of a day with only rain decreases from 56% to 49%, the chance of a day with mixed snow and rain remains an essentially constant 2% throughout, and the chance of a day with only snow remains an essentially constant 1% throughout.
Probability of Precipitation in December
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 December in West Lake Sammamish is rapidly decreasing, starting the month at 8.4 inches, when it rarely exceeds 13.0 inches or falls below 3.9 inches, and ending the month at 7.2 inches, when it rarely exceeds 11.0 inches or falls below 3.7 inches.
Average Monthly Rainfall in December
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. As with rainfall, we consider the liquid-equivalent snowfall accumulated over a sliding 31-day period centered around each day.
The average sliding 31-day liquid-equivalent snowfall during December in West Lake Sammamish is essentially constant, remaining about 0.2 inches throughout, and rarely exceeding 0.9 inches or falling below -0.0 inches.
The highest average 31-day liquid-equivalent accumulation is 0.2 inches on December 29.
Average Monthly Liquid-Equivalent Snowfall in December
Over the course of December in West Lake Sammamish, the length of the day is essentially constant. The shortest day of the month is December 21, with 8 hours, 26 minutes of daylight and the longest day is December 1, with 8 hours, 42 minutes of daylight.
Hours of Daylight and Twilight in December
The earliest sunrise of the month in West Lake Sammamish is 7:36 AM on December 1 and the latest sunrise is 20 minutes later at 7:56 AM on December 31.
The earliest sunset is 4:16 PM on December 10 and the latest sunset is 10 minutes later at 4:27 PM on December 31.
Daylight saving time is observed in West Lake Sammamish during 2020, but it neither starts nor ends during December, so the entire month is in standard time.
For reference, on June 20, the longest day of the year, the Sun rises at 5:10 AM and sets 15 hours, 59 minutes later, at 9:09 PM, while on December 21, the shortest day of the year, it rises at 7:53 AM and sets 8 hours, 26 minutes later, at 4:19 PM.
Sunrise & Sunset with Twilight in December
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 West Lake Sammamish is essentially constant during December, remaining around 0% throughout.
For reference, on August 5, 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.
Humidity Comfort Levels in December
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 West Lake Sammamish is essentially constant during December, remaining within 0.1 miles per hour of 5.2 miles per hour throughout.
For reference, on December 3, the windiest day of the year, the daily average wind speed is 5.3 miles per hour, while on August 1, the calmest day of the year, the daily average wind speed is 2.7 miles per hour.
The highest daily average wind speed during December is 5.3 miles per hour on December 3.
Average Wind Speed in December
The hourly average wind direction in West Lake Sammamish throughout December is predominantly from the south, with a peak proportion of 53% on December 1.
Wind Direction in December
West Lake Sammamish 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 West Lake Sammamish is gradually decreasing during December, falling by 2°F, from 49°F to 47°F, over the course of the month.
Average Water Temperature in December
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 West Lake Sammamish typically lasts for 8.4 months (257 days), from around March 6 to around November 19, rarely starting before February 11 or after April 1, and rarely ending before October 28 or after December 18.
The month of December in West Lake Sammamish is more likely than not fully outside of the growing season, with the chance that a given day is in the growing season rapidly decreasing from 30% to 2% over the course of the month.
Time Spent in Various Temperature Bands and the Growing Season in December
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.
The average accumulated growing degree days in West Lake Sammamish are essentially constant during December, remaining within 3°F of 2,146°F throughout.
Growing Degree Days in December
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 West Lake Sammamish is essentially constant during December, remaining around 0.9 kWh throughout.
The lowest average daily incident shortwave solar energy during December is 0.9 kWh on December 24.
Average Daily Incident Shortwave Solar Energy in December
For the purposes of this report, the geographical coordinates of West Lake Sammamish are 47.578 deg latitude, -122.101 deg longitude, and 318 ft elevation.
The topography within 2 miles of West Lake Sammamish contains very significant variations in elevation, with a maximum elevation change of 968 feet and an average elevation above sea level of 252 feet. Within 10 miles contains very significant variations in elevation (2,959 feet). Within 50 miles contains large variations in elevation (8,901 feet).
The area within 2 miles of West Lake Sammamish is covered by artificial surfaces (35%), water (29%), and trees (26%), within 10 miles by artificial surfaces (39%) and trees (36%), and within 50 miles by trees (54%) and artificial surfaces (13%).
This report illustrates the typical weather in West Lake Sammamish 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 West Lake Sammamish.
For each station, the records are corrected for the elevation difference between that station and West Lake Sammamish 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 West Lake Sammamish is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between West Lake Sammamish and a given station.
The stations contributing to this reconstruction are: Renton Municipal Airport (78%, 13 kilometers, southwest); Snohomish County Airport (Paine Field) (19%, 39 kilometers, north); and Stampede Pass (3.2%, 67 kilometers, southeast).
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 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.
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.