Average Weather at Juneau International Airport Alaska, United States

1. World
2. United States
3. Alaska
4. Juneau City and Borough
5. Juneau International Airport

At Juneau International Airport, the summers are cool; the winters are long, freezing, and windy; and it is wet and overcast year round. Over the course of the year, the temperature typically varies from 25°F to 65°F and is rarely below 7°F or above 75°F.

The warm season lasts for 3.5 months, from May 20 to September 6, with an average daily high temperature above 58°F. The hottest day of the year is July 30, with an average high of 65°F and low of 51°F.

The cold season lasts for 4.1 months, from November 9 to March 13, with an average daily high temperature below 39°F. The coldest day of the year is December 31, with an average low of 25°F and high of 32°F.

The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.

At Juneau International Airport, the average percentage of the sky covered by clouds experiences mild seasonal variation over the course of the year.

The clearer part of the year at Juneau International Airport begins around February 16 and lasts for 6.6 months, ending around September 3. On May 26, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 32% of the time, and overcast or mostly cloudy 68% of the time.

The cloudier part of the year begins around September 3 and lasts for 5.5 months, ending around February 16. On October 5, the cloudiest day of the year, the sky is overcast or mostly cloudy 81% of the time, and clear, mostly clear, or partly cloudy 19% of the time.

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days at Juneau International Airport varies significantly throughout the year.

The wetter season lasts 5.6 months, from August 19 to February 7, with a greater than 58% chance of a given day being a wet day. The chance of a wet day peaks at 74% on October 10.

The drier season lasts 6.4 months, from February 7 to August 19. The smallest chance of a wet day is 42% on May 27.

Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 73% on October 10.

Rainfall

To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. Juneau International Airport experiences extreme seasonal variation in monthly rainfall.

Rain falls throughout the year at Juneau International Airport. The most rain falls during the 31 days centered around October 6, with an average total accumulation of 15.1 inches.

The least rain falls around June 9, with an average total accumulation of 4.2 inches.

Snowfall

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. Colder, drier snow tends to be on the higher end of that range and warmer, wetter snow on the lower end.

As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day of the year. Juneau International Airport experiences extreme seasonal variation in monthly liquid-equivalent snowfall.

The snowy period of the year lasts for 5.9 months, from October 16 to April 12, with a sliding 31-day liquid-equivalent snowfall of at least 0.1 inches. The most snow falls during the 31 days centered around January 20, with an average total liquid-equivalent accumulation of 2.3 inches.

The snowless period of the year lasts for 6.1 months, from April 12 to October 16. The least snow falls around July 17, with an average total liquid-equivalent accumulation of 0.0 inches.

The length of the day at Juneau International Airport varies extremely over the course of the year. In 2017, the shortest day is December 21, with 6 hours, 22 minutes of daylight; the longest day is June 21, with 18 hours, 18 minutes of daylight.

The earliest sunrise is at 3:50 AM on June 18, and the latest sunrise is 4 hours, 56 minutes later at 8:47 AM on December 27. The earliest sunset is at 3:05 PM on December 15, and the latest sunset is 7 hours, 3 minutes later at 10:09 PM on June 23.

Daylight saving time (DST) is observed at Juneau International Airport during 2017, starting in the spring on March 12, lasting 7.8 months, and ending in the fall on November 5.

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 perceived humidity level at Juneau International Airport, as measured by the percentage of time in which the humidity comfort level is muggy, oppressive, or miserable, does not vary significantly over the course of the year, remaining a virtually constant 0% throughout.

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 Juneau International Airport experiences significant seasonal variation over the course of the year.

The windier part of the year lasts for 5.6 months, from October 9 to March 28, with average wind speeds of more than 4.2 miles per hour. The windiest day of the year is January 1, with an average hourly wind speed of 5.9 miles per hour.

The calmer time of year lasts for 6.4 months, from March 28 to October 9. The calmest day of the year is July 4, with an average hourly wind speed of 2.5 miles per hour.

The predominant average hourly wind direction at Juneau International Airport varies throughout the year.

The wind is most often from the south for 4.5 months, from May 29 to October 15, with a peak percentage of 45% on September 17. The wind is most often from the east for 7.5 months, from October 15 to May 29, with a peak percentage of 49% on January 1.

Juneau 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 water temperature experiences some seasonal variation over the course of the year.

The time of year with warmer water lasts for 2.5 months, from July 4 to September 18, with an average temperature above 52°F. The day of the year with the warmest water is August 10, with an average temperature of 55°F.

The time of year with cooler water lasts for 4.8 months, from December 10 to May 3, with an average temperature below 44°F. The day of the year with the coolest water is March 4, with an average temperature of 40°F.

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 experiences extreme seasonal variation over the course of the year.

The brighter period of the year lasts for 3.2 months, from April 26 to July 31, with an average daily incident shortwave energy per square meter above 4.2 kWh. The brightest day of the year is June 12, with an average of 5.2 kWh.

The darker period of the year lasts for 4.3 months, from October 11 to February 20, with an average daily incident shortwave energy per square meter below 1.3 kWh. The darkest day of the year is December 22, with an average of 0.2 kWh.

For the purposes of this report, the geographical coordinates of Juneau International Airport are 58.355 deg latitude, -134.576 deg longitude, and 69 ft elevation.

The topography within 2 miles of Juneau International Airport contains very significant variations in elevation, with a maximum elevation change of 1,765 feet and an average elevation above sea level of 133 feet. Within 10 miles contains very significant variations in elevation (5,820 feet). Within 50 miles also contains extreme variations in elevation (8,451 feet).

The area within 2 miles of Juneau International Airport is covered by trees (30%), sparse vegetation (29%), and water (21%), within 10 miles by trees (35%) and water (26%), and within 50 miles by trees (28%) and water (24%).

This report illustrates the typical weather at Juneau 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 Point

Juneau 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 are Angoon Seaplane Base, Hoonah Airport, Gustavus Airport, Haines Airport, Skagway Airport, and Sitka Rocky Gutierrez Airport.

Other Data

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.