Summer (June to August) is the obvious time to visit Kokkola. Days are long — in June there is almost no true darkness this far north — the archipelago is accessible, Ohtakari beach is active, and the Kokkola Opera festival in July is the cultural highlight of the year. The Tankar island ferry only runs in summer.
Winter is cold and often snowy, with short days, but the city has its own cold-season character. The Kokkola Winter Accordion Festival (usually February or March) brings a warm, noisy contrast to the frozen landscape outside. The surrounding coastline in winter, with sea ice forming in the bay and the light going pink and gold in the early afternoon, has a genuine bleakness that winter travellers appreciate.
Spring (May) and early autumn (September) are pleasant but quiet, with cooler temperatures and fewer visitors. Autumn colours in the forests inland are worth seeing in early October.