Summer is the peak travel season in Alaska. The weather is warmest and it can stay light through most of the night. Summer is when seasonal fishing begins and is a time when popular spots like Denali National Park open to the public.
May and September are considered shoulder months by the tourist industry. These are the months in between the popular summer and winter travel season, when there are few crowds and travel to Alaska is cheaper. May is usually drier (ranging from 0.16 inches in Barrow to 9 inches in Yakutat) than September, which can get frequent rain (averaging 0.95 inches in Fairbanks to 18 inches in Yakutat).
April, October, and November are the transitional months from summer to winter. It can be particularly muddy in April, when the snow is still melting. In October/November, the snow is just arriving. However, depending where you are staying, it may be still too early to enjoy winter snow-related activities. Annette averages just 0.2 inches in October while snowy Valdez receives an average of 42 inches of snow in November.
Winter, particularly late winter in February and March, is a great time to enjoy winter carnivals and dog mushing in addition to the famed Aurora Borealis (or Northern Lights)--a display of lights considered a space phenomenon and only visible in northern latitudes.
For visitors wanting to experience Alaska's long hours of daylight during the night, consider visiting Fairbanks, which on June 21 has about 22 hours of daylight.