Average Weather in December at Portage, Portage Glacier Alaska, United States
Daily high temperatures decrease by 2°F, from 28°F to 26°F, rarely falling below 9°F or exceeding 42°F.
Daily low temperatures decrease by 3°F, from 16°F to 14°F, rarely falling below -9°F or exceeding 32°F.
For reference, on July 14, the hottest day of the year, temperatures at Portage, Portage Glacier typically range from 44°F to 58°F, while on January 13, the coldest day of the year, they range from 13°F to 26°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 at Portage, Portage Glacier experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 72% throughout the month. The highest chance of overcast or mostly cloudy conditions is 74% on December 18.
The clearest day of the month is December 1, with clear, mostly clear, or partly cloudy conditions 30% of the time.
For reference, on December 18, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 74%, while on March 16, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 38%.
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. At Portage, Portage Glacier, the chance of a wet day over the course of December is essentially constant, remaining around 57% throughout.
For reference, the year's highest daily chance of a wet day is 60% on September 28, and its lowest chance is 40% on June 24.
Over the course of December at Portage, Portage Glacier, the chance of a day with only rain decreases from 10% to 6%, the chance of a day with mixed snow and rain increases from 23% to 27%, and the chance of a day with only snow remains an essentially constant 24% 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 at Portage, Portage Glacier is essentially constant, remaining about 4.1 inches throughout, and rarely exceeding 9.0 inches or falling below 0.5 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 at Portage, Portage Glacier is essentially constant, remaining about 4.0 inches throughout, and rarely exceeding 6.9 inches or falling below 1.8 inches.
The highest average 31-day liquid-equivalent accumulation is 4.2 inches on December 16.
Average Monthly Liquid-Equivalent Snowfall in December
Over the course of December at Portage, Portage Glacier, the length of the day is gradually decreasing. From the start to the end of the month, the length of the day decreases by 28 minutes, implying an average daily decrease of 57 seconds, and weekly decrease of 6 minutes, 38 seconds.
The shortest day of the month is December 21, with 5 hours, 36 minutes of daylight and the longest day is December 1, with 6 hours, 14 minutes of daylight.
Hours of Daylight and Twilight in December
The earliest sunrise of the month at Portage, Portage Glacier is 9:37 AM on December 1 and the latest sunrise is 30 minutes later at 10:06 AM on December 26.
The earliest sunset is 3:40 PM on December 16 and the latest sunset is 11 minutes later at 3:51 PM on December 31.
Daylight saving time is observed at Portage, Portage Glacier 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 4:21 AM and sets 19 hours, 11 minutes later, at 11:32 PM, while on December 22, the shortest day of the year, it rises at 10:05 AM and sets 5 hours, 36 minutes later, at 3:42 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 at Portage, Portage Glacier 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 at Portage, Portage Glacier is gradually increasing during December, increasing from 7.6 miles per hour to 8.1 miles per hour over the course of the month.
For reference, on January 8, the windiest day of the year, the daily average wind speed is 8.4 miles per hour, while on June 26, the calmest day of the year, the daily average wind speed is 5.0 miles per hour.
Average Wind Speed in December
Wind Direction in December
Portage, Portage Glacier 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 Portage, Portage Glacier is gradually decreasing during December, falling by 3°F, from 41°F to 38°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 at Portage, Portage Glacier typically lasts for 2.9 months (89 days), from around June 3 to around August 31, rarely starting before May 11 or after July 9, and rarely ending before August 1 or after September 25.
The month of December at Portage, Portage Glacier 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 at Portage, Portage Glacier are essentially constant during December, remaining around 199°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 at Portage, Portage Glacier is essentially constant during December, remaining around 0.2 kWh throughout.
The lowest average daily incident shortwave solar energy during December is 0.1 kWh on December 21.
Average Daily Incident Shortwave Solar Energy in December
For the purposes of this report, the geographical coordinates of Portage, Portage Glacier are 60.783 deg latitude, -148.833 deg longitude, and 1,355 ft elevation.
The topography within 2 miles of Portage, Portage Glacier contains extreme variations in elevation, with a maximum elevation change of 3,360 feet and an average elevation above sea level of 899 feet. Within 10 miles also contains extreme variations in elevation (5,991 feet). Within 50 miles also contains extreme variations in elevation (10,568 feet).
The area within 2 miles of Portage, Portage Glacier is covered by shrubs (33%), trees (21%), water (16%), and sparse vegetation (14%), within 10 miles by snow and glaciers (26%) and shrubs (21%), and within 50 miles by shrubs (22%) and water (20%).
This report illustrates the typical weather at Portage, Portage Glacier 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
Portage, Portage Glacier 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 Whittier Airport, Palmer Municipal Airport, Seward Airport, Birchwood Airport, Bryant Army Heliport, New Wasilla Airport, Elmendorf Air Force Base, and Merrill Field Airport.
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.