The Interior region of Alaska has a highly continental climate, with the warmest summers in the state, as well as the lowest record winter temperatures. Mean annual temperatures average slightly below freezing, with individual years at some stations being above freezing. In general, the Interior ecosystem is spruce-dominated: black spruce and spaghnum moss on poorly drained permafrost with a thin active layer (muskeg) and white spruce on the better drained uplands. Disturbed areas have a fireweed - willow - birch/aspen/alder - spruce succession. Permafrost is discontinuous and easily disturbed by fire or human activity. Tree line is on the order of 1000 meters elevation or lower, sloping downward toward the west and north.
Station location on the map above is incomplete and of limited accuracy. On this scale, Fairbanks is co-located with University. Northway I believe is off the south edge of the map, south and a little west of Eagle. Farewell is not far from McGrath, and McKinley is SSW of the "B" in Big Delta. Tanana is west and a little north of Fairbanks. I'll get a new map in soon.
Technically the region is bounded by the watersheds of the Brooks Range to the north and the Alaska Range (including the highest peaks in North America) to the south. In practice, there are no long-term stations above tree line. The climate actually measured is that of the valleys, especially the broad valleys of the Yukon, Tanana and Kuskokwim Rivers. Minimum temperatures are strongly controlled by ground-based inversions, and thus may vary radically over short distances and in response to human modification of the local environment.
The region covers a large area and has a correspondingly large number of stations. Half of these (Big Delta, Eagle, Fairbanks, McKinley, Northway and University, all in the southeastern quarter of the region) can be reached by road; the other half (Allakaket, Bettles, Farewell, Holy Cross, McGrath and Tanana) can be reached only by air, water, or cross country. Of the latter three, only Bettles, McGrath and Tanana are still operating.
Although there are 12 stations in the Interior, there was only one year
in which all 12 actually produced mean annual temperatures. In order to
produce an adjusted average for the region, the three stations with the
most missing data (Eagle, Farewell, and Allakaket) were dropped before the
years with data from all 9 remaining stations were used to produce an average
temperature for each station. Individual station deviations from these means
were then averaged and added to the average of the normals for all 9 stations
to produce this regional temperature history. The red circles are individual
years; the blue line is a 5-point binomially weighted running mean.
Because there are so many stations in the region, I have broken the region into sections to plot neighboring stations together. The two upper valley stations, near the Canadian border, are Northway in the Tanana valley and Eagle in the Yukon valley. Neither of these stations has recorded a mean annual temperature above freezing.
The lower valley comparison involves Holy Cross, almost on the Yukon delta, and Farewell, somewhat farther inland and having a very short record.
Bettles and Allakaket are both near the south flanks of the Brooks Range. Allakaket is almost on the Arctic Circle; Bettles is slightly farther north and east. The two stations are separated by roughly 40 miles. Mean annual temperatures above freezing have not been recorded at these two stations.
The remaining stations were plotted together, though the resulting plot is badly crowded. Note that McKinley, one of the higher stations, is often warmer than others on the mean annual temperature, even though its summer temperatures are among the cooler ones. Tanana and McGrath, the two stations lowest in elevation, are often among the colder sites. This is due to the dominance of ground-based temperature inversions at night and during the winter months. The warm period around 1940 and the warming around 1976 also show clearly on this figure.
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