Climate of Alaska
TOPOGRPHIC FEATURES – Alaska is the westernmost extension of the North American Continent. Its east-west span covers a distance of 2,000 miles, and from north to south a distance of 1,100 miles. The State’s coastline, 33,000 miles in length, is 50 percent longer than that of the conterminous United States. In addition to the Aleutian Islands, hundreds of other islands, mostly undeveloped, are found along the northern coast of the Gulf of Alaska, the Alaska Peninsula, and the Bering Sea Coast. Alaska contains 375 million acres of land and many thousands of lakes.
There are 12 major rivers plus three major tributaries of the Yukon, all of which drain two-thirds of the State. Four rivers, the Yukon, Stikine, Alek, and Taku, can be classed as major international rivers.
The two longest mountain ranges are the Brooks Range which separates the Arctic region from the interior and the Alaska-Aleutian Range which extends westward along the Alaska Peninsula and the Aleutian Islands, and northward about 200 miles from the Peninsula, then eastward to Canada. Other shorter but important ranges are the Chugach Mountains which form a rim to the central north Gulf of Alaska, and the Wrangell Mountains lying to the northeast of the Chugach Range and south of the Alaska Range. Both of these shorter ranges merge with the St. Elias Mountains, extending southeastward through Canada and across southeastern Alaska as the Coast Range. Numerous peaks in excess of 10,000 feet are found in all but the Brooks Range. The highest peak (20,320 feet above sea level) in the North American Continent, Mt. McKinley, is located in south-central Alaska. Many other peaks tower above 16,000 feet; however, nearly all of the inhabited sections of the State are at 1,000 feet elevation or less.
Permafrost is a major factor in the geography of Alaska. It is defined as a layer of soil at variable depths beneath the surface of the earth in which the temperature has been below freezing continuously from a few several thousands of years. It exists where summer heating fails to penetrate to the base of the layer of frozen ground. Permafrost covers most of the northern third of the State. Discontinuous or isolated patches also exist over the central portions in an overall area covering nearly a third of the State. No permafrost exists in the south-central and southern coastal portions including southeastern Alaska, the Alaska Peninsula, and the Aleutian chain.
CLIMATIC ZONES – The geographical features already mentioned have a significant effect on Alaska’s climate, which falls into five major zones. Reference is made to the section of maps at the back, specifically to the map showing geographical subdivisions of Alaska. The climate zones are: (1) a maritime Zone which includes southeastern Alaska, the south coast, and southwestern islands; (2) a maritime continental zone which includes the western portions of Bristol Bay and west-central zones. In this zone the summer temperatures are moderated by the open waters of the Bering Sea, but winter temperatures are more continental in nature due to the presence of sea ice during the coldest months of the year; (3) a transition zone between the maritime and continental zones in the southern portion of the Copper River zone, the Cook Inlet zone, and the northern extremes of the south coast zone; (4) a continental zone make up of the remainders of the Copper River and west-central divisions, and the interior basin; and (5) an artic zone, shown on the map as the arctic drainage division.
PRECIPITATION – In the maritime zone a coastal mountain range coupled with plentiful moisture produces annual precipitation amounts up to 200 inches in the southeastern panhandle, and up to 150 inches along the northern coast of the Gulf of Alaska. Amounts decrease to near 60 inches on the southern side of the Alaska Range in the Alaska Peninsula and Aleutian Island sections. Precipitation amounts decrease rapidly to the north, with an average of 12 inches in the continental zone and less than 6 inches in the arctic region.
Snowfall makes up a large portion of the total annual precipitation. For example, Yakutat averages 216 inches of snow annually and has a total annual precipitation (rain plus water equivalent of snow) of about 130 inches. Along the arctic slope, Barrow receives an average of 29 inches of snow annually and a total annual precipitation of slightly more than 4 inches. Total snow depths on the ground are controlled by the temperature of an area. Fortunately, most of the areas of heavy snow have relatively mild temperatures which prevent total depths from becoming excessive. Present-day snow removal equipment is able to keep highways and airports operational.
Precipitation extremes are of interest. With reference to total amounts (both rain and snow) and based on existing records, the greatest annual precipitation occurred at MacLeod Harbor on Montague Island in the Gulf of Alaska with 332.29 inches in 1976. This station also holds the record for monthly totals with 70.99 inches in November 1976.
The record maximum for 24 hours occurred on December 29, 1955, in the city of Cordova (North Gulf of Alaska coast) with a measured amount of 14.13 inches. Snowfall extremes are all credited to a station at Thompson Pass, which is on the highway north of Valdez. The record measurements are: season (1952-53) 974.5 inches; month (February 1953) 298 inches; and 24-hour (December 1955) 62 inches.
TEMPERATURE – Mean annual temperatures in Alaska range from the low 40’s under the maritime influence in the south to a chilly 10 degrees a long the Arctic Slope north of the Brooks Mountain Range. The greatest seasonal temperature contrast between seasons is found in the central and eastern portion of the continental interior. In this area summer heating produces average maximum temperatures in the upper 70’s with extreme readings in the 90’s. The highest recorded temperature for the state is 100 degrees at Fort Yukon in June 1915. In winter the lack of sunshine permits radiation to lower temperatures to the minus 50’s and occasionally colder for two or three weeks at a time. Average winter minimums in this area are 20 to 30 degrees below zero. The coldest temperature ever recorded in Alaska was minus 80 degrees at Prospect Creek on January 23, 1971.
Elsewhere in the state, temperature contrasts are much more moderate. In the maritime zone the summer to winter range of average temperatures in from near 60 to the 20’s. In the transition zone, temperatures range from the low 60’s to near zero; in the maritime-continental zones the range is from the low 60’s to 10 below zero. The arctic slopes has a range extending form the upper 40’s to 20 below zero.
Winter temperatures play a principal role in the flow of most of Alaska’s rivers. Usually beginning in late October and extending into May (and sometimes early June for the northernmost steams), thick layers of ice form, permitting passage with all types of heavy equipment. In many areas construction work and oil exploration is done in winter because both the ground and the streams are frozen hard enough from the use of the heaviest of equipment. Several rivers cease to flow completely during the coldest months.
WIND – A normal storm track along the Aleutian Island chain, the Alaska Peninsula, and all of the coastal area of the Gulf of Alaska exposes these parts of the state to a large majority of the storms crossing the North Pacific, resulting in a variety of wind problems. Direct exposure results in the frequent occurrence of winds in excess of 50 mph during all but the summer months. Shemya, on the western end of the Aleutian Islands, has experienced winds on an estimated 139 mph (estimated because the wind recorder pen could only record up to 128 mph). Wind velocities approaching 100 mph are not common but do occur, usually associated with mountainous terrain and narrow passes. For years, strong winds have taken their toll of both merchant and fishing vessels.
An occasional storm will either develop in or move into the Bering Sea then move north or northeastward, creating strong winds along the western coastal area. Because of the low flat ground in many places along the coast, these winds will cause flooding during the time the winds are blowing onshore. Winter storms moving eastward across the southern Arctic Ocean cause winds of 50 mph or higher along the arctic coast. Except for local strong wind conditions, winds are generally light in the interior sections.
Strong winds, or in fact any wind occurring in the areas of extreme winter cold, create a definite hazard to personnel exposed for even brief periods of time. For example, (using a wind chill chart developed by the U.S. Army) a temperature of a -13°F and an accompanying wind of 15 mph equals conditions that would be experienced with a temperature of –49 °F and no wind. If the temperature is a -49° F and the winds 10 mph, the resulting equivalent temperature is -81° F.
