Yellowknife's high season splits into two distinct windows: summer (mid-June through August) and aurora season (late August through March). The choice depends entirely on what you are after.
Summer brings long days — up to 20-plus hours of daylight around the solstice — and mild temperatures in the 20s Celsius. This is the time for canoeing, hiking, fishing, and outdoor festivals. The Folk on the Rocks music festival in July is one of Canada's best northern cultural events. The downside is mosquitoes, which can be ferocious in June and July.
Winter is cold and dark but has its own fierce appeal. The northern lights are the main draw, and a clear night in January with the aurora dancing overhead is one of the most extraordinary natural sights in Canada. Average temperatures from November to February hover around minus 25 to minus 35, and minus 40 is not unusual. Come prepared with serious gear. The Long John Jamboree in March — with dogsled races, ice fishing derbies, and outdoor festivities — celebrates the end of winter with great energy.