Winters in Bad Oeynhausen are mild, with temperatures rarely dropping below freezing and averaging around 3-5°C. Spring brings a steady warming trend, with March marking the beginning of more consistent warmth, reaching averages of 7°C. Summer is warm but not hot, with July and August highs often peaking at around 25-26°C. Autumn sees a gentle cooling, with temperatures gradually dropping back to around 4-11°C by October. December's chill brings an end to the year, with temperatures averaging around 4°C.