Summer (June–early September) is when Karlovac is at its best. Daytime temperatures sit comfortably in the high twenties, and the rivers turn the city into a place for swimming and lazy afternoons on the bank. The Karlovac Beer Days festival in late August or early September is one of central Croatia's bigger street parties.
Spring and autumn give cooler walks along the river paths and shorter queues for the museums. Winters can be cold and damp — the city is at the foothills of the Karst, and snow is not uncommon.