 Daily high temperatures range from 9 to 29 ° F ( − 13 to − 2 ° C ) in winter to 80 to 90 ° F ( 27 to 32 ° C ) in summer , while lower elevations can experience conditions over 100 ° F ( 38 ° C ) . Idaho 's mountain ranges can block Arctic air in the winter , but when cold air masses do enter the area , they sometimes <unk> in the Snake and Salmon river valleys , causing very cold temperatures to persist . Summer and fall are generally dry , while intense short @-@ duration thunderstorms can occur in late spring and early summer as atmospheric moisture interacts with warm temperatures and steep topography via <unk> lifting . During winter , warm , moist air from the Pacific Ocean often brings rain at lower elevations in addition to snowfall throughout the forest . The influence of these Pacific maritime air masses increases as latitude increases in the forest . Average annual snowfall ranges from 55 inches ( 140 cm ) in drier areas and at lower elevations to 70 inches ( 180 cm ) in wetter locations and higher elevations . The growing season within the forest ranges from over 150 days in lower elevations to less than 30 days in alpine areas . 
