Winters in Otaru are harsh and cold, with temperatures often dropping below -20°C in January and February. Spring brings a gradual warming trend, with temperatures rising to around 7-8°C by April. Summer is mild to warm, with July and August averaging highs of around 23-25°C. Autumn sees a return to cooler temperatures, with September and October averaging highs of around 18-20°C. December's temperature fluctuates wildly, often dipping below -20°C but occasionally reaching as high as 15°C.