Climate of Interior Alaska
Interior Alaskan forests are part of the circumpolar band of boreal forests. Interior Alaska is bounded on the south by the Alaska Range and on the north by the Brooks Range, mountains that provide an effective barrier to coastal air masses. As a result, the climate is strongly continental with cold winters and warm relatively dry summers. These forests are also unique for their association with an environment characterized by drastic seasonal fluctuation in day length (more than 21 hours on June 21 and less than 3 hours on December 21). Mean annual temperatures in the Tanana valley area average between -2 degC and -5 degC with the long-term average at the Fairbanks International Airport being -3.1 degC. Temperature ranges from extremes of -50 degC in January to over +33 degC in July, with a short growing season (100 days or less). The average annual precipitation is only 269 mm with 30% falling as snow. Snow covers the ground from mid-October until mid- to late April, and maximum accumulation averages 75-100 cm. Summer and winter precipitation is generated from major frontal systems that cross the State, but convection storms that produce abundant lightning add significantly to the summer precipitation. Although precipitation amounts during the growing season may be low, evaporation rates are also low because of the relative short growing season and cool temperatures. Even so, as much as 76 to 100 percent of the summer precipitation may be lost as evapotranspiration.
Since the mid-20th century, interior Alaska has warmed approximately 2.5 degC.
Temperature records from the Fairbanks International Airport record (mid 1948 to present; from Alaska Climate Research Center).
Climate records combined with dendrochronological climate reconstructions based on d13C of tree rings indicate that the rate and length of time summers have been warming in Fairbanks is unprecedented over the past several centuries:
Long-term reconstruction of summer (May - August) temperature in interior Alaska (from Barber et al. 2004. Climate Change).
Overall, growing seasons have lengthened by 2.5 days/decade (Keyser et al. 2000) to approximately 125 frost free days presently.