The Southwestern Islands includes the tip of the Alaska peninsula (Cold Bay), the islands in the Bering Sea (St Paul) and the Aleutian chain (Adak, Shemya, and Attu), stretching across the 180th meridian toward Siberia. All of the stations are coastal, located near sea level. Southwestern is the most maritime region of the state, and the most dependant on military and Coast Guard stations for formal weather reports, especially in the Aleutians themselves. It is also the only region of Alaska on a more westerly time zone than the mainland: Aleutian time is based on the 150th Meridian. Since the Aleutians stretch more than 30 degrees of longitude west of that meridian, solar noon can be more than 2 hours after clock noon. However, the extreme maritime climate tends to minimize both diurnal and annual temperature cycles. This is the home of the Aleutian Low, the heart of the North Pacific extratropical storm belt. The local economy is based almost entirely on fishing, and weather information here is critical locally as well as globally.
Although mean annual temperatures are above freezing (except
for the eastern Bering Sea, where sea ice forms annually over the shallow
continental shelf of Beringia) summers are too cold and windy for strong
forest growth. The ecology is basically Arctic, with grassy tundra dominating.
How much of the treelessness is imposed by the climate and how much is due
to the fact that trees were unable to reach the islands when temperatures
rose after the last ice age is controversial. Transplanted trees in some
of the eastern Aleutians appeared to be growing well until recently. The
island terrain is rugged, dominated by young and often active volcanoes
- hardly surprising, as the Aleutian chain marks the line where the Pacific
Plate plunges deeply enough beneath the North American plate that subducted
crust begins to melt and rise as magma to the surface.
The adjusted annual temperature, below, was calculated by using the years for which data were available from every station but Attu, where missing data is a major problem. This period was used as a base to calculate a normal temperature for each of the remaining four stations, and a full-length anomaly series based on these normals were also calculated for each of the stations. The anomalies for the four stations were then averaged, year by year, and added to the averaged normal.
Note that the information prior to 1940 is based entirely on St Paul Island.