Alaska has four different climatic zones: maritime, continental, transitional, and Arctic. Kodiak, the Aleutians, and southeastern and south central Alaska have a climate primarily influenced by the sea, so that temperatures do not vary greatly throughout the year, but rainfall is quite heavy and frequent. Western Alaska, a transitional climate, has much lower temperatures and less rainfall, but, like the Aleutians, frequent periods of extremely high winds and blowing snow. Arctic Alaska has very little snowfall, cool summer temperatures, and frequent high winds, particularly from the east. The interior has a continental climate characterized by extremely great temperature variations, but only moderate rain and snow.
The average January temperatures in southeastern Alaska are close to freezing, but snowfall in many areas can be high. Rainfall, particularly along the coasts, can exceed 2,500 mm (100 in) a year. South central Alaska has a maritime climate, ranging northward into a transitional climate.
The climates of Homer and Kodiak are more similar to southeastern Alaska’s climate than to that of Anchorage. Because of the oceans and the mountains, and the storms coming from the Gulf of Alaska, this region shows considerable variation from place to place in rainfall and snowfall. For example, Thompson Pass, north of Valdez, has recorded more than 6 m (20 ft) of snowfall in one winter, whereas Anchorage often has little snow all winter long. Under proper conditions, however, cold air from the interior can cross the mountains and bring temperatures in the upper -20°s C (lower -20°s F) to this region.
The Aleutians, dominated by perpetual low pressure systems and contrasting ocean currents, have frequent fogs, high winds or “williwaws,” and rainstorms, making the region extremely difficult for both vessel and aircraft transportation. The interior has a continental (also called sub-Arctic or taiga) climate caused by being in the rain shadow of the coast ranges and inland. Winter cold spells can last several weeks, with temperatures recorded in the -50°s C (-60°s F), while summer temperatures, particularly in the Yukon Flats, can reach into the upper 30°s C (upper 90°s F). Summers are characterized by frequent thunderstorms, which often cause forest fires. Mean annual precipitation is about 380 to 510 mm (about 15 to 20 in), with winter snowfalls varying significantly from year to year but averaging in lowland areas at about 1,300 mm (about 50 in).
Western Alaska, from the Alaska Peninsula northward to the southern Seward Peninsula, has a transitional climate, one influenced by frequent low pressure systems from the Bering Sea, but also by cold air from the interior and winter sea ice conditions. The result is summer temperatures that seldom rise much above 10°C (50°F), and winter conditions characterized by high winds and snow storms. Arctic Alaska, stretching from the northern Seward Peninsula (Kotzebue Sound) northward to Barrow and eastward to Demarcation Point, has an Arctic climate characterized by low winter and summer temperatures and frequent high winds.
While snowfall is low, generally less than 300 mm (12 in), blowing snow frequently creates a condition known as whiteout, in which people cannot differentiate between land and sky, making it extremely easy to become disoriented and lost. Summers are cool, with temperatures generally less than 10°C (50°F) and rainfall tends to concentrate in late summer. The high winds along the coast of the Beaufort Sea blow away insects and make the area favorable to caribou in the summer months. Because of Alaska’s high northern latitude, the length of day varies much more between summer and winter than it does in other parts of the United States. At Fort Yukon, on the Arctic Circle, the sun barely rises above the southern horizon on the shortest day of the year, December 21. At Barrow, on the Arctic Coast, the sun is not seen from late November until late January. In summer the days are much longer and Alaska is as much “the land of the midnight sun” as are Norway and Sweden. At Barrow there is continuous daylight from early May to early August. © "United States" © Emmanuel Buchot and Encarta
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