June, July, and August are the practical months for visiting. The roads are clear, the days are essentially endless (no real darkness from mid-May to mid-August), boats run to Hornstrandir, and the Við Djúpið music festival fills the town with concerts. Temperatures hover between 8 and 14 °C — cool by southern standards, but Iceland's warmest stretch.
Winter is a different proposition. Snow piles up on the harbour, daylight shrinks to a few twilit hours, and avalanches occasionally close the only road in or out. Northern lights are likely on clear nights. The small ski hill at Tungudalur runs from January to April. For anyone wanting to see Isafjordur at its most extreme, late February — when the sun first returns above the mountain ridges — is locally celebrated with the Sólarkaffi (sun coffee).