Using the climatic signal-noise ratio, as well as other tests, dates have been detected around which important changes in Northeasterly and Westerly circulation have been observed in mid-latitude South America. These changes in zonal circulation intensity which occur, on average, in periods of 10 years or more, have been generally coincident with those registered in the Northern Hemisphere, in the last century. The Westerly intensities series show climatic jumps along six months of the calendar year. Information on those registered in July of 1939, 1949, 1967 and 1977 and January 1974 is included. Climatic jumps were observed in Northeasterly intensities in the monthly and seasonal scales, respectively, with no effect upon the annual values. An important change in average conditions of the North-easterlies detected at the beginning of the 1950s, and fluctuations of low frequency, might be the cause of outstanding precipitation jumps in the Argentina's subtropical area, where abundant (scanty) precipitation was associated with strong (weak) Northeasterlies.