Climate and Average Weather Year Round in Unalaska Alaska, United States
In Unalaska, the summers are short, cold, and windy; the winters are long, very cold, wet, and extremely windy; and it is overcast year round. Over the course of the year, the temperature typically varies from 30°F to 56°F and is rarely below 21°F or above 62°F.
Based on the tourism score, the best time of year to visit Unalaska for warm-weather activities is for the entire month of August.
Climate in Unalaska
Average Temperature in Unalaska
The warm season lasts for 2.6 months, from June 30 to September 16, with an average daily high temperature above 52°F. The hottest day of the year is August 14, with an average high of 56°F and low of 49°F.
The cold season lasts for 4.8 months, from November 26 to April 19, with an average daily high temperature below 40°F. The coldest day of the year is January 23, with an average low of 30°F and high of 36°F.
Average High and Low Temperature in Unalaska
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 in Unalaska
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
In Unalaska, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.
The clearer part of the year in Unalaska begins around August 31 and lasts for 3.0 months, ending around November 29. On October 14, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 41% of the time, and overcast or mostly cloudy 59% of the time.
The cloudier part of the year begins around November 29 and lasts for 9.0 months, ending around August 31. On July 17, the cloudiest day of the year, the sky is overcast or mostly cloudy 82% of the time, and clear, mostly clear, or partly cloudy 18% of the time.
Cloud Cover Categories in Unalaska
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. The chance of wet days in Unalaska varies throughout the year.
The wetter season lasts 5.8 months, from September 1 to February 24, with a greater than 36% chance of a given day being a wet day. The chance of a wet day peaks at 47% on December 17.
The drier season lasts 6.3 months, from February 24 to September 1. The smallest chance of a wet day is 25% on May 5.
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 43% on November 10.
Daily Chance of Precipitation in Unalaska
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. Unalaska experiences significant seasonal variation in monthly rainfall.
Rain falls throughout the year in Unalaska. The most rain falls during the 31 days centered around December 9, with an average total accumulation of 4.0 inches.
The least rain falls around April 25, with an average total accumulation of 1.7 inches.
Average Monthly Rainfall in Unalaska
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. Unalaska experiences some seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 4.7 months, from November 21 to April 11, 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 27, with an average total liquid-equivalent accumulation of 0.7 inches.
The snowless period of the year lasts for 7.3 months, from April 11 to November 21. The least snow falls around August 6, with an average total liquid-equivalent accumulation of 0.0 inches.
Average Liquid-Equivalent Monthly Snowfall in Unalaska
The length of the day in Unalaska varies extremely over the course of the year. In 2021, the shortest day is December 21, with 7 hours, 24 minutes of daylight; the longest day is June 20, with 17 hours, 7 minutes of daylight.
Hours of Daylight and Twilight in Unalaska
The earliest sunrise is at 5:34 AM on June 17, and the latest sunrise is 3 hours, 51 minutes later at 9:24 AM on December 28. The earliest sunset is at 4:44 PM on December 13, and the latest sunset is 5 hours, 58 minutes later at 10:41 PM on June 24.
Daylight saving time (DST) is observed in Unalaska during 2021, starting in the spring on March 14, lasting 7.8 months, and ending in the fall on November 7.
Sunrise & Sunset with Twilight and Daylight Saving Time in Unalaska
The figure below presents a compact representation of key lunar data for 2021. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases.
Moon Rise, Set & Phases in Unalaska
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 Unalaska, 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 in Unalaska
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 Unalaska experiences extreme seasonal variation over the course of the year.
The windier part of the year lasts for 7.6 months, from September 13 to May 2, with average wind speeds of more than 15.7 miles per hour. The windiest day of the year is November 25, with an average hourly wind speed of 20.2 miles per hour.
The calmer time of year lasts for 4.4 months, from May 2 to September 13. The calmest day of the year is July 18, with an average hourly wind speed of 11.2 miles per hour.
Average Wind Speed in Unalaska
The predominant average hourly wind direction in Unalaska varies throughout the year.
The wind is most often from the east for 6.0 days, from February 16 to February 22, with a peak percentage of 27% on February 16. The wind is most often from the north for 3.4 months, from February 22 to June 5 and for 1.8 months, from December 22 to February 16, with a peak percentage of 34% on April 20. The wind is most often from the west for 6.5 months, from June 5 to December 22, with a peak percentage of 44% on August 29.
Wind Direction in Unalaska
Unalaska 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 2.4 months, from July 15 to September 28, with an average temperature above 47°F. The day of the year with the warmest water is August 21, with an average temperature of 49°F.
The time of year with cooler water lasts for 4.6 months, from December 28 to May 16, with an average temperature below 41°F. The day of the year with the coolest water is March 16, with an average temperature of 39°F.
Average Water Temperature in Unalaska
Best Time of Year to Visit
To characterize how pleasant the weather is in Unalaska throughout the year, we compute two travel scores.
The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit Unalaska for general outdoor tourist activities is for the entire month of August, with a peak score in the third week of August.
Tourism Score in Unalaska
The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit Unalaska for hot-weather activities is from August 10 to August 19.
Beach/Pool Score in Unalaska
For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.
Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.
Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.
Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.
Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.
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 Unalaska typically lasts for 6.4 months (195 days), from around April 29 to around November 10, rarely starting before April 8 or after May 20, and rarely ending before October 16 or after December 9.
Time Spent in Various Temperature Bands and the Growing Season in Unalaska
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.
Growing Degree Days in Unalaska
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 3.4 months, from April 25 to August 6, with an average daily incident shortwave energy per square meter above 3.9 kWh. The brightest day of the year is May 30, with an average of 4.8 kWh.
The darker period of the year lasts for 3.7 months, from October 27 to February 17, with an average daily incident shortwave energy per square meter below 1.3 kWh. The darkest day of the year is December 16, with an average of 0.4 kWh.
Average Daily Incident Shortwave Solar Energy in Unalaska
For the purposes of this report, the geographical coordinates of Unalaska are 53.874 deg latitude, -166.537 deg longitude, and 26 ft elevation.
The topography within 2 miles of Unalaska contains very significant variations in elevation, with a maximum elevation change of 1,850 feet and an average elevation above sea level of 255 feet. Within 10 miles contains very significant variations in elevation (3,547 feet). Within 50 miles also contains extreme variations in elevation (5,971 feet).
The area within 2 miles of Unalaska is covered by water (55%), grassland (19%), and shrubs (14%), within 10 miles by water (41%) and shrubs (24%), and within 50 miles by water (86%).
This report illustrates the typical weather in Unalaska, 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 is only a single weather station, Unalaska Airport, in our network suitable to be used as a proxy for the historical temperature and dew point records of Unalaska.
At a distance of 2 kilometers from Unalaska, closer than our threshold of 150 kilometers, this station is deemed sufficiently nearby to be relied upon as our primary source for temperature and dew point records.
The station records are corrected for the elevation difference between the station and Unalaska according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.
Please note that the station records themselves may additionally have been back-filled using other nearby stations or the MERRA-2 reanalysis.
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 airports 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.