Bahía Blanca's climate is humid subtropical under the Köppen climate classification. The climate is influenced by the location of the city by the ocean with warm superficial streams by the shores. Since the city is located in the limit between Pampas and Patagonia, it is warm and more humid to the north and rapidly becomes drier to the south.
Temperature extremes are notably frequent when compared to other cities in the Pampa region: daytime temperatures tend to reach very high values in the summer, and nighttimes lows can be very cold in the winter. Summer brings thunderstorms and temperatures usually in the 30 to 35 °C (86 to 95 °F) range, although 43.8 °C (110.8 °F) has been recorded, with nights between 14 and 18 °C (57 and 64 °F). Southerly winds often bring much cooler weather for short periods. Fall begins in March, and by late April the first frosty mornings may occur. During the winter, the weather is often dryer, high temperatures average 10 to 16 °C (50 to 61 °F) and nights from 0 to 6 °C (32 to 43 °F). Temperatures often drop below freezing: values of −6 °C (21 °F) are recorded often, and during stronger cold waves temperatures have plummeted to under −10 °C (14 °F).
Average rainfall is on the threshold of 615 millimetres (24 in) per year. Snow is not very common in the city (the last significant snowfall took place recently in July 2009. The one before was on May 2007), although it sometimes does snow in Sierra de la Ventana. Summers are hot. March, September, October and November are months when most of rainfall is expected. Autumn and winter tend to be windy. It should be kept in mind that the city is located in the southern (austral) hemisphere: summer starts on 21 December ending 21 March. Winter starts on 21 June ending on 21 September
