The South region is located below the Tropic of Capricorn, in a temperate zone. It is influenced by the system of disturbed circulation of the South, which produces the rains, mainly in the summer. It is also influenced by the system of disturbed circulation of the West, that brings rains and storms, sometimes hail, producing winds with bursts of 60 to 90 km/h (37.3 to 55.9 mph). Regarding temperatures: the winter is mild and the summer is hot. The annual medium temperatures range from 14 to 22 °C (57.2 to 71.6 °F), and in places with altitudes above 1,100 m (3,609 ft), drops to approximately 10 °C (50 °F). Some parts of the southern region also have an oceanic climate.
In the summer, mainly in January, in the valleys of the rivers Paranapanema, Paraná and Ibicuí-Jacuí, the medium temperature is in excess of 24 °C (75.2 °F), and the medium temperature of the river Uruguay surpasses 26 °C (78.8 °F). The average maximum temperature stays around 24 to 27 °C (75.2 to 80.6 °F) on the elevated surfaces of the plateau and, in the lowest areas, between 30 and 32 °C (86 and 89.6 °F).
In the winter, mainly in July, the medium temperature stays relatively low, oscillating between 10 and 15 °C (50 and 59 °F), except for the valleys of the rivers Paranapanema and Paraná, besides the coast of Paraná and Santa Catarina, where the averages are approximately 15 to 18 °C (59 to 64.4 °F). The average maximum temperature is also low, around 20 to 24 °C (68 to 75.2 °F), in the big valleys and in the coast, and 16 to 20 °C (60.8 to 68 °F) in the plateau region. The average minimum temperature varies from 6 to 12 °C (42.8 to 53.6 °F) , and the thermometer frequently registers temperatures near 0|ºC, sometimes even reaching negative indexes, accompanied by frost and snow, in consequence of the invasion of polar masses.
The annual medium pluviosity oscillates from 1,250 to 2,000 mm (49.2 to 78.7 in), except along the coast of Paraná and west of Santa Catarina, where the values are in excess of 2,000 mm (78.7 in), and in the north of Paraná and in a small coastal area of Santa Catarina, which have lower recordings down to 1,250 mm (49.2 in). The maximum pluviometric indexes occur in the winter and the minimum in the summer throughout almost the whole area.