Average Weather in Ketchikan Alaska, United States
In Ketchikan, the temperature typically varies from 31°F to 65°F over the course of the year, and is rarely below 19°F or above 72°F.
The warm season lasts for 3.1 months, from June 7 to September 9, with an average daily high temperature above 59°F. The hottest day of the year is July 31, with an average high of 65°F and low of 54°F.
The cold season lasts for 4.3 months, from November 10 to March 20, with an average daily high temperature below 44°F. The coldest day of the year is January 1, with an average low of 31°F and high of 38°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 Ketchikan varies extremely over the course of the year. In 2017, the shortest day is December 21, with 7 hours, 6 minutes of daylight; the longest day is June 21, with 17 hours, 27 minutes of daylight.
Hours of Daylight and Twilight
The earliest sunrise is at 4:04 AM on June 17, and the latest sunrise is 4 hours, 10 minutes later at 8:13 AM on December 28. The earliest sunset is at 3:15 PM on December 13, and the latest sunset is 6 hours, 17 minutes later at 9:32 PM on June 23.
Daylight saving time (DST) is observed in Ketchikan 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 Ketchikan, 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 Ketchikan begins around April 23 and lasts for 5.1 months, ending around September 25. On August 2, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 42% of the time, and overcast or mostly cloudy 58% of the time.
The cloudier part of the year begins around September 25 and lasts for 6.9 months, ending around April 23. On December 10, the cloudiest day of the year, the sky is overcast or mostly cloudy 79% of the time, and clear, mostly clear, or partly cloudy 22% 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 Ketchikan varies significantly throughout the year.
The wetter season lasts 7.1 months, from September 5 to April 7, with a greater than 56% chance of a given day being a wet day. The chance of a wet day peaks at 73% on October 31.
The drier season lasts 4.9 months, from April 7 to September 5. The smallest chance of a wet day is 40% on June 6.
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 71% on October 22.
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. Ketchikan experiences very significant seasonal variation in monthly rainfall.
Rain falls throughout the year in Ketchikan. The most rain falls during the 31 days centered around October 22, with an average total accumulation of 13.7 inches.
The least rain falls around June 26, with and average total accumulation of 4.4 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. Ketchikan experiences some seasonal variation in monthly liquid-equivalent snowfall.
The snowy period of the year lasts for 4.7 months, from November 5 to March 26, 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 13, with an average total liquid-equivalent accumulation of 0.6 inches.
The snowless period of the year lasts for 7.3 months, from March 26 to November 5. The least snow falls around July 27, 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 Ketchikan, 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 Ketchikan experiences mildly seasonal variation over the course of the year.
The windier part of the year lasts for 6.4 months, from October 6 to April 19, with average wind speeds of more than 3.8 miles per hour. The windiest day of the year is January 2, with an average hourly wind speed of 4.9 miles per hour.
The calmer time of year lasts for 5.6 months, from April 19 to October 6. The calmest day of the year is July 19, with an average hourly wind speed of 2.7 miles per hour.
Average Wind Speed
The predominant average hourly wind direction in Ketchikan varies throughout the year.
The wind is most often from the south for 6.9 months, from April 6 to November 3, with a peak percentage of 46% on October 8. The wind is most often from the east for 5.1 months, from November 3 to April 6, with a peak percentage of 54% on January 10.
Ketchikan 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 1 to September 16, with an average temperature above 53°F. The day of the year with the warmest water is August 8, with an average temperature of 56°F.
The time of year with cooler water lasts for 4.7 months, from December 6 to April 27, with an average temperature below 45°F. The day of the year with the coolest water is March 6, with an average temperature of 42°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 3.4 months, from May 2 to August 13, with an average daily incident shortwave energy per square meter above 4.2 kWh. The brightest day of the year is June 16, with an average of 5.3 kWh.
The darker period of the year lasts for 4.2 months, from October 16 to February 21, with an average daily incident shortwave energy per square meter below 1.3 kWh. The darkest day of the year is December 20, with an average of 0.3 kWh.
Average Daily Incident Shortwave Solar Energy
For the purposes of this report, the geographical coordinates of Ketchikan are 55.342 deg latitude, -131.648 deg longitude, and 269 ft elevation (map ).
The topography within 2 miles of Ketchikan contains large variations in elevation, with a maximum elevation change of 2,838 feet, and an average elevation above sea level of 398 feet. Within 10 miles contains extreme variations in elevation (3,297 feet). Within 50 miles also contains extreme variations in elevation (4,977 feet).
The area within 2 miles of Ketchikan is covered by trees (61%) and water (29%), within 10 miles by trees (55%) and water (37%), and within 50 miles by trees (48%) and water (41%).
This report illustrates the typical weather in Ketchikan, 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 Ketchikan.
For each station, the records are corrected for the elevation difference between that station and Ketchikan 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 Ketchikan is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Ketchikan and a given station.
The stations contributing to this reconstruction are: Ketchikan International Airport (86%, 4.4 kilometers, west) and Metlakatla Seaplane Base (14%, 24 kilometers, south).
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 .