The Interior region of Alaska has a highly continental climate with the warmest summers in the state, as well as the lowest recorded 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 3000 ft elevation or lower, sloping downward toward the west and north.
Technically the region is bounded by the watersheds of the Brooks Range to the north and the Alaska Range to the south. In practice, there are no long-term stations above tree line. The climate actually observed 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.
Click to learn more about the observing stations in:
Bettles
Big Delta
Fairbanks
McGrath