Harstad has two very different personalities depending on season. Summer (June through August) brings the midnight sun — continuous daylight from late May to mid-July — and the Arctic Arts Festival in June. This is the busiest tourist season and the most immediately dramatic period to visit.
Winter (November through March) brings darkness and the best chance of northern lights. Orca sightings peak in November and December when killer whales follow herring into the fjords. The cold is real — temperatures regularly drop below -10°C — but the scenery in snow and the spectacle of an Arctic winter make it worthwhile for prepared travellers. September and October are a good compromise: some remaining daylight, reasonable chance of northern lights, fewer tourists, and the autumn colours on the surrounding hillsides.