Average Weather in Juneau Alaska, United States
In Juneau, the temperature typically varies from 20°F to 61°F over the course of the year, and is rarely below 2°F or above 70°F.
The warm season lasts for 3.5 months, from May 22 to September 8, with an average daily high temperature above 54°F. The hottest day of the year is July 31, with an average high of 61°F and low of 48°F.
The cold season lasts for 4.1 months, from November 10 to March 12, with an average daily high temperature below 35°F. The coldest day of the year is December 31, with an average low of 20°F and high of 28°F.
Average High and Low Temperature
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.
Average Hourly Temperature
The length of the day in Juneau 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, 17 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 3:50 AM on June 18, and the latest sunrise is 4 hours, 55 minutes later at 8:46 AM on December 27. The earliest sunset is at 3:05 PM on December 15, and the latest sunset is 7 hours, 2 minutes later at 10:08 PM on June 23.
Daylight saving time (DST) is observed in Juneau during 2017, starting in the spring on March 12, lasting 7.8 months, and ending in the fall on November 5.
Sunrise & Sunset with Twilight and Daylight Saving Time
In Juneau, 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 in Juneau begins around February 16 and lasts for 4.9 months, ending around July 12. On May 15, 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 July 12 and lasts for 7.1 months, ending around February 16. On October 8, 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 in Juneau 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 in Juneau changes throughout the year.
Rain alone is the most common for 8.2 months, from March 18 to November 22. The highest chance of a day with rain alone is 72% on October 10.
Mixed snow and rain is the most common for 2.5 months, from February 10 to March 18 and from November 22 to January 1. The highest chance of a day with mixed snow and rain is 27% on December 7.
Snow alone is the most common for 1.3 months, from January 1 to February 10. The highest chance of a day with snow alone is 25% on January 19.
Daily Chance of Precipitation
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 in the year. Juneau experiences very significant seasonal variation in monthly rainfall.
Rain falls throughout the year in Juneau. The most rain falls during the 31 days centered around October 5, with an average total accumulation of 15.0 inches.
The least rain falls around June 9, with and average total accumulation of 4.3 inches.
Average Monthly Rainfall
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 in the year. Juneau experiences very significant seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 7.1 months, from October 2 to May 6, 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 12, with an average total liquid-equivalent accumulation of 4.8 inches.
The snowless period of the year lasts for 4.9 months, from May 6 to October 2. The least snow falls around July 23, with an average total liquid-equivalent accumulation of 0.0 inches.
Average Liquid-Equivalent Monthly Snowfall
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 in Juneau, 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.
Humidity Comfort Levels
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 experiences significant seasonal variation over the course of the year.
The windier part of the year lasts for 5.6 months, from October 10 to March 28, with average wind speeds of more than 4.0 miles per hour. The windiest day of the year is January 1, with an average hourly wind speed of 5.7 miles per hour.
The calmer time of year lasts for 6.4 months, from March 28 to October 10. The calmest day of the year is July 4, with an average hourly wind speed of 2.5 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in Juneau varies throughout the year.
The wind is most often from the south for 4.7 months, from May 27 to October 19, with a peak percentage of 47% on October 4. The wind is most often from the east for 7.3 months, from October 19 to May 27, with a peak percentage of 49% on January 18.
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 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 5, with an average temperature of 41°F.
Average Water Temperature
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 significant seasonal variation over the course of the year.
The brighter period of the year lasts for 3.1 months, from April 26 to July 29, 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 19, with an average daily incident shortwave energy per square meter below 1.2 kWh. The darkest day of the year is December 20, with an average of 0.2 kWh.
Average Daily Incident Shortwave Solar Energy
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, 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 .