June - August
Anchorage is the hub for almost all Alaska travel three months a year, from approximately June 15 to Sept. 15. More than half the city’s roughly 1 million visitors arrive during this period, which offers usually reliable weather (daytime highs in the low 70s, partly sunny weather interspersed with periods of scattered showers). Summer-season travelers will find very high hotel and rental-car rates (more than twice those of October and April), troops of retirees strolling the downtown streets, and buses of cruise passengers extending their voyages onshore. On the plus side, in June and early July, the light hardly fades—you can schedule a long bike ride after dinner if you like, and it’s possible to wind up a golf game at midnight.
October - April
Winter can be a delightful time to visit Anchorage, particularly late February through mid-April, when the sun returns from the low horizon, the ski-tracks are long set on the city’s trails, the skiing is best at Alyeska, and prices, crowds and tour-bus tomfoolery are at their lowest. (Exceptions are the Fur Rendezvous in February, and Iditarod Trail Race in early March.) Although Alaska is famously fearsomely cold, this rap is overstated—in Anchorage, a cold day in March is likely 10-25 degrees, and visitors may encounter extended periods of sunny weather. Yes, you can see northern lights in Anchorage (though Fairbanks is a better bet) and the Chugach and Kenai Mountains never look so glorious as when lit by late-afternoon winter sun. As for December and early January—Alaskans go to Hawaii.
Mid-April to mid-June, and Labor Day - Oct. 15
Things get interesting in Anchorage in these two bracket periods. Will it freeze in September, or be sunny and warm? Will Alyeska still be open in May so energetic types can ski, fish and golf all in the same day? Both months bring cruise and tour-bus crowds into town periodically; rates adjust downward; salmon shows up in local restaurants in May and holds through October—pretty much the same as decent weather.