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 summers that are relatively dry. These forests are unique for their association with an environment characterized by drastic seasonal fluctuations in day length (more than 21 hours on June 21 and less than three hours on December 21). Mean annual temperatures in the Tanana Valley of Interior Alaska average between -2 °C and -5 °C, with the long-term average at the Fairbanks International Airport being -3.1 °C. Temperatures range from extremes of -50 °C in January to over +33°C in July, and growing seasons are short (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 summer precipitation. Although precipitation amounts during the growing season may be low, evaporation rates are also low because of the relatively short growing season and cool temperatures. Even so, as much as 76 to 100 percent of the summer precipitation may be lost as evapotranspiration.

Changing Climate

Alaska has warmed at twice the rate as the rest of the U.S. over the past 60 years. This has involved more extremely hot days and fewer extremely cold days. Such changes in temperature have resulted in earlier snowmelt, increasing wildfire size and frequency, and warmer permafrost, just to name a few. With climate change, annual average temperature is expected to continue increasing in Alaska. Precipitation is also expected to increase during all seasons, but the state will still likely become drier due to longer growing seasons and rising temperatures.