The Rosario area has a Pampean Humid subtropical climate (Köppen climate classification Cwa), and is well known for its changeable weather conditions. The city has average temperatures of 23.4 °C (74 degrees Fahrenheit) maximum and 11.6 °C (53 °F) minimum. The annual rainfall is 1,038 mm (40.9 in).
Rosario is usually warmer than other mainland Argentine capital cities in the winter. The lowest average on winter is 4.4 °C (40 °F). This is due in part to the city's flat topography, its situation on the Paraná River bank, and the presence of high density of urbanization. Those facto have created a microclimate known as urban heat island that often means that the city is significantly warmer than its surrounding rural areas.
The temperature difference usually is larger at night than during the day and larger in winter than in summer, and is most apparent when winds are weak. However, snowfalls are extremely rare: the most recent occurrence of sleet in the CBD was on 9 July 2007. During the spring, Rosario commonly enjoys extended periods of mild weather and clear skies. On average, Rosario has average day-night temperatures of 23–10 °C (73–50 °F). However, it occasionally experiences hotter and drier summer days, with maximum temperatures above 35 °C (95 °F), when northerly winds blow dry air from Brazil. The record high temperature is 42.4 °C (108.3 °F). The record low is −11.1 °C (12.0 °F)
