Fort Yukon is obviously a very cold and dry place. Iron Mountain is considerably wetter and warmer, but its annual precipitation is still less than that typical of the Eastern Deciduous Forest. The tundra to the north is even colder and drier than the climate at Fort Yukon. Indeed precipitation levels in the northern half of the Northern Boreal Forest and the Tundra are equivalent to those of the deserts of the United States and northern Mexico. The Northern Boreal Forest, in short, is dry and cool.
Cool air holds less water than warm air and, consequently there is less water to form precipitation.
Moist, warm air from the Gulf of Mexico rarely reaches this far north and moisture laden air from the Pacific dumps most of its water along the Pacific Coast because of the mountain ranges in the region and the rapidly cooling temperatures as one moves inland. The description of the Northern Boreal Forest as a place of little precipitation poses a contradiction, however. There is no single answer, but a number of factors figure into the equation. The Northern Boreal Forest is located in an area of flat topography and water does not run off readily. Water evaporates more rapidly in warm area than in cool air.