Alaska State Climate

Climate Map OVERVIEW Alaska’s 17 degrees of latitude—by far the highest of any state—sprawls over five distinct climatic zones. The state's geography—including over 33,000 miles (53,100 km) of coastline, 12 major rivers, many of the country's tallest mountain peaks, and a large permafrost region—shape Alaska's weather. The climate is quite varied throughout this enormous state, and temperature and precipitation can be extreme. SEASONS Winter’s notorious stretches of 24-hour darkness only occur in the state’s far north; the season brings weak, limited sunshine in the main population areas further south. While temperatures along the southern and southeastern coasts can stay relatively mild, in the 20s F (about -7°C to -2°C), they routinely fall into the -40s F or -50s F (-40°C to -50°C) in the interior. The average winter temperature along the arctic slope is -20 F (-29°C). Snow is heaviest in this season, with the highest amounts falling on the mountains near the southern coast. Long, Cold, Dark Nights in Winter Spring arrives fully by late May, when sunlight hours are long and most of the state enjoys clear skies and warm daily temperatures. This pattern extends through June, then changes as the summer rainy season approaches. Summer marks the beginning of the rainy season and is characterized by prolonged sunlight and the state’s balmiest temperatures. Just after the summer solstice on June 21, Alaska’s southernmost areas receive 18 hours of daily sunlight, while the northernmost settlements experience 24-hour sunshine. Temperatures statewide range from the 60s F to the 80s F, occasionally reaching the 90s F (32°C to 36°C). Autumn features heavy rainfall as temperatures begin their descent toward winter lows. The days become markedly shorter as the season moves toward the winter solstice on December 21. In higher latitudes and altitudes, snow begins to fall as colder arctic air meets moist air off the Gulf of Alaska. TEMPERATURE Mendenhall Glacier on a Bright Spring Day With its maritime climate, the southeastern Alaskan Panhandle is the mildest temperature zone, ranging from an average near the 60s F (about 14°C to 15°C) in summer to the 20s F (about -7°C to -2°C) in winter. In contrast, average temperatures in the extreme north along the Arctic Ocean range from the upper 40s F (about 8°C or 9°C) in summer to -20F (-29°C) in winter. The range of temperatures in the interior can be described simply as hot to cold. Summer readings often reach the 90s F (32°C to 37°C), with a seasonal average in the high 70s F (25°C to 26°C). (The state’s all-time high of 100°F/38°C was set in the deep interior at Fort Yukon, 125 miles northeast of Fairbanks.) In winter, lack of sunlight can allow temperatures to plummet into the -50s F (-46°C to -50°C) or even colder for weeks at a time. PRECIPITATION Precipitation Map The statewide rainfall average is 22.7 inches (577 mm), making Alaska the 39th wettest U.S. state. Rain and snow fall in successively drier bands moving north. The south and southeast are very wet, while the interior is much drier. The extreme north is a classic desert where fewer than 5 inches of rain fall per year. The relatively mild southeast and south coast receive up to 200 inches (5,080 mm) and 150 inches (3,810 mm) of snow and rain per year, respectively, while the interior receives about 12 inches (305 mm) and the arctic region less than 6 inches (152 mm). It’s useful to remember that the arctic region is considered a desert because of its very low levels of precipitation. Juneau has 221 days of precipitation per year, while Barrow in the extreme north has 78. The rainfall difference between the two cities is also instructive: Juneau receives 58.33 inches (1,482 mm) of rain per year while Barrow receives 4.16 inches (106 mm). The figures for Anchorage, Alaska’s largest city, are somewhat in between: 16.08 inches (408 mm) of rain and 117 days of total precipitation per year. Dry Climate of the Arctic Region Alaska’s extremes of precipitation match its reputation as a state of superlatives. Its driest spot, the northern community of Kuparuk, has an annual average rainfall of 3.61 inches (91.7 mm), while Little Port Walter in the southeast holds the annual average rainfall record at 225.35 inches (5,724 mm). The greatest annual downpour was recorded in 1976 at MacLeod Harbor in the Gulf of Alaska when 332.29 inches (8,440 mm or 27.7 feet) fell. The same location holds the all-time monthly figure, 70.99 inches (1,803 mm or 5.2 feet), set in the same year.  The highest average annual snowfall is also in the southeast, at Thompson Pass: 551.5 inches (14,008 mm)—almost 46 feet. Thompson Pass also holds the all-time snowfall record for one year, 974.4 inches (24,750 mm), or 81 feet, set in 1952–53, as well as the all-time monthly figure of 298 inches (7,569 mm/24.8 feet) during the same season. The all-time one-day snowfall record of 62 inches (1,575 mm/5.2 feet) is also held by Thompson Pass.  HUMIDITY Rainy Day in Whittier Humidity is greatest in the southeast, where Juneau has a year-round average of 80 percent in the morning and 69 percent in the afternoon (figures that are almost exactly the same as Key West, Florida’s). Anchorage, further north and west, has an average morning humidity of 73 percent and an afternoon average of 63 percent, corresponding roughly to Boston, Massachusetts’ figures. Fairbanks, deep in the northern interior, is the driest of Alaska’s major cities, with an average morning humidity of 69 percent and an afternoon humidity of 57 percent. The least humid part of the state is in the far north, past the Arctic Circle, where desert-like conditions prevail. SUNSHINE Overcast Day in Valdez Despite summer sunlight reaching 19.5 hours per day in Anchorage, 21 hours in Fairbanks, and 24 hours at the Arctic Ocean, Alaska is not generally a sunny state. Anchorage has 61 clear days, 65 partly cloudy days, and 239 cloudy days per year. The respective numbers for Fairbanks are 70, 86, and 210, while Juneau’s figures are 44, 41, and 280. The settlement with the highest number of clear days is Kotzebue, a town just above the Arctic Circle on the Bering Sea. Cold Bay, near the extreme southwestern end of the Alaska Peninsula, is the state’s cloudy-day record holder at 304 per year.  REGIONS First Winter Snowfall on the Chugach Mountains Alaska’s has five distinct climatic zones: a mild, mid-latitude oceanic climate (sometimes called maritime) in the southeast, along the south coast, and on the southwestern islands; a more extreme continental maritime zone along the Bering Sea; a transition zone between maritime and continental with subarctic features in the interior; a continental zone in the south-central and interior regions; and a frigid arctic zone in the far north. WEATHER EXTREMES Floods in Alaska tend to be very localized events, often caused by rain squalls or thawing rivers where the breakup of ice suddenly releases large volumes of water. The state’s major river, the Yukon, is the waterway most susceptible to flooding. But it stretches east to west across the middle of the state, a virtually unpopulated area, so much of its floods have little direct effect. Volcanoes in Alaska are often active—50 of its 130 volcanoes and volcanic fields have experienced activity within the past 200 years. Minor eruptions can create temporary changes in local weather conditions. Major eruptions can have far-flung, temporary effects on the seasons, for instance cooling spring and summer in the Lower 48 states. Blizzards often occur in the far north when high winds combine with loose snow to create blinding conditions. Blizzard Conditions Thunderstorms north of the Brooks Range on the arctic slope are rare. Most thunderstorms are of short duration, usually lasting about 20 minutes, and occur in the state’s interior. Lightning-caused fires are a major factor in the destruction of about one million acres of forest per year in the state. Winds along the shore can be strong, and North Pacific storms routinely track across the Aleutian Islands, the Alaska Peninsula, and into the Gulf of Alaska. The highest recorded winds have been in the Aleutians, around 139 mph (225 kph), and wind velocities of 100 mph (162 kph) are not uncommon in the mountains. The interior is generally free of high-wind conditions. One of the greatest dangers wind poses in Alaska is wind chill. For example a 15 mph (24 kph) wind can make a-13°F (-25°C) temperature the equivalent of -49°F (-45°C) INTERESTING FACTS Despite Alaska’s far north location, it ranks fifth in the United States in the range between its all-time high and low temperatures. The state’s 180°F (100°C) temperature range trails Montana (187°F/86°C), Utah (186°F/86°C), and Wyoming and North Dakota (both at 181°F/83°C). The now-abandoned settlement of Prospect Creek, an Alaskan Pipeline construction camp located almost exactly on the Arctic Circle, recorded the coldest temperature ever in U.S. history on January 23, 1971: -80°F (-62°C). However, no major Alaska city ranks among the top 10 coldest U.S. cities in terms of lowest annual average temperatures. Three of the 10 U.S. cities that experience the greatest annual temperature range are in Alaska: Fairbanks (number one at 90.8°F), Bettles (number two at 90°F), and McGrath (number seven at 86.2°F). -World Trade Press