Inuvik has two real seasons and two short transitions between them — and which one you want depends on what you have come for.
Summer (June–early August) is the time of the midnight sun — 56 days when the sun does not set. Temperatures climb into the high teens (°C); the delta opens up; the Dempster Highway is at its driest. It is also when the Great Northern Arts Festival runs in mid-July and when mosquitoes are at their worst. The flat light of 2 a.m. takes some getting used to; the windows of most hotels have heavy curtains.
Aurora season (late August–mid-April) brings the northern lights, the dog-sledding, and the ice road to Aklavik. The deep winter months are punishingly cold (-30°C and worse, multiple weeks below -40°C). February and March are the sweet spot — long nights for the lights, days starting to return, temperatures slightly less brutal.
Shoulder seasons (May, September–October) are short and difficult: break-up and freeze-up mean roads, ferries, and ice crossings are all unreliable. Aim for one of the two main seasons rather than around them.