Average Weather in December in Juneau Alaska, United States
Daily high temperatures decrease by 2°F, from 31°F to 28°F, rarely falling below 14°F or exceeding 39°F.
Daily low temperatures decrease by 3°F, from 24°F to 20°F, rarely falling below 2°F or exceeding 34°F.
For reference, on July 31, the hottest day of the year, temperatures in Juneau typically range from 48°F to 61°F, while on December 31, the coldest day of the year, they range from 20°F to 28°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 Juneau experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 77% throughout the month.
The clearest day of the month is December 31, with clear, mostly clear, or partly cloudy conditions 25% of the time.
For reference, on October 8, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 81%, while on May 15, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 32%.
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 Juneau, the chance of a wet day over the course of December is decreasing, starting the month at 65% and ending it at 61%.
For reference, the year's highest daily chance of a wet day is 74% on October 10, and its lowest chance is 42% on May 27.
Over the course of December in Juneau, the chance of a day with only rain decreases from 19% to 15%, the chance of a day with mixed snow and rain decreases from 26% to 23%, and the chance of a day with only snow increases from 20% to 23%.
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 Juneau is rapidly decreasing, starting the month at 7.9 inches, when it rarely exceeds 14.9 inches or falls below 2.5 inches, and ending the month at 6.3 inches, when it rarely exceeds 11.9 inches or falls below 1.8 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 Juneau is increasing, starting the month at 3.7 inches, when it rarely exceeds 7.0 inches or falls below 1.7 inches, and ending the month at 4.6 inches, when it rarely exceeds 7.3 inches or falls below 2.1 inches.
Average Monthly Liquid-Equivalent Snowfall in December
Over the course of December in Juneau, the length of the day is gradually decreasing. From the start to the end of the month, the length of the day decreases by 24 minutes, implying an average daily decrease of 48 seconds, and weekly decrease of 5 minutes, 35 seconds.
The shortest day of the month is December 21, with 6 hours, 22 minutes of daylight and the longest day is December 1, with 6 hours, 54 minutes of daylight.
Hours of Daylight and Twilight in December
The earliest sunrise of the month in Juneau is 8:19 AM on December 1 and the latest sunrise is 27 minutes later at 8:46 AM on December 27.
The earliest sunset is 3:05 PM on December 15 and the latest sunset is 10 minutes later at 3:15 PM on December 31.
Daylight saving time is observed in Juneau during 2019, but it neither starts nor ends during December, so the entire month is in standard time.
For reference, on June 21, the longest day of the year, the Sun rises at 3:51 AM and sets 18 hours, 17 minutes later, at 10:07 PM, while on December 22, the shortest day of the year, it rises at 8:45 AM and sets 6 hours, 22 minutes later, at 3:07 PM.
Sunrise & Sunset with Twilight and Daylight Saving Time 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 Juneau is essentially constant during December, remaining around 0% throughout.
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 Juneau is essentially constant during December, remaining within 0.2 miles per hour of 10.3 miles per hour throughout.
For reference, on January 1, the windiest day of the year, the daily average wind speed is 10.5 miles per hour, while on July 4, the calmest day of the year, the daily average wind speed is 4.6 miles per hour.
Average Wind Speed in December
The hourly average wind direction in Juneau throughout December is predominantly from the east, with a peak proportion of 47% on December 31.
Wind Direction in December
Juneau 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 Juneau is essentially constant during December, remaining within 1°F of 43°F throughout.
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 Juneau typically lasts for 4.4 months (135 days), from around May 14 to around September 26, rarely starting before April 27 or after May 31, and rarely ending before September 6 or after October 16.
The month of December in Juneau is reliably fully outside of the growing season.
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 Juneau are essentially constant during December, remaining around 348°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 Juneau is essentially constant during December, remaining around 0.3 kWh throughout.
The lowest average daily incident shortwave solar energy during December is 0.2 kWh on December 22.
Average Daily Incident Shortwave Solar Energy in December
For the purposes of this report, the geographical coordinates of Juneau are 58.302 deg latitude, -134.420 deg longitude, and 1,047 ft elevation.
The topography within 2 miles of Juneau contains extreme variations in elevation, with a maximum elevation change of 3,504 feet and an average elevation above sea level of 895 feet. Within 10 miles also contains extreme variations in elevation (5,453 feet). Within 50 miles also contains extreme variations in elevation (8,409 feet).
The area within 2 miles of Juneau is covered by trees (38%), water (26%), and shrubs (23%), within 10 miles by trees (30%) and water (23%), and within 50 miles by trees (28%) and water (24%).
This report illustrates the typical weather in Juneau 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 2 weather stations near enough to contribute to our estimation of the temperature and dew point in Juneau.
For each station, the records are corrected for the elevation difference between that station and Juneau 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 Juneau is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Juneau and a given station.
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.
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.