Midlatitude disturbances such as intense cold fronts and cutoff lows are a very important cause of severe-weather events over the southern part of South America, particularly during the austral winter months. Behind cold fronts, cold air from higher latitudes is forced to flow equatorward to the east of the Andes. Occasionally fronts might produce cold surges in tropical latitudes, with freezing temperatures (referred as to GEADAS in Portuguese) over crop-growing areas of southern, southeastern, and central Brazil. The structure and dynamical processes of winter synoptic-scale waves associated with cold surges over South America are documented in this paper. It is shown that the rotated extended empirical orthogonal function technique is capable of extracting well-defined regional patterns from 850-hPa meridional-wind perturbation fields. Over South America, waves behave very differently in the lower and middle troposphere: while upper-level waves propagate northeastward as they cross the Andes, ... Abstract Midlatitude disturbances such as intense cold fronts and cutoff lows are a very important cause of severe-weather events over the southern part of South America, particularly during the austral winter months. Behind cold fronts, cold air from higher latitudes is forced to flow equatorward to the east of the Andes. Occasionally fronts might produce cold surges in tropical latitudes, with freezing temperatures (referred as to GEADAS in Portuguese) over crop-growing areas of southern, southeastern, and central Brazil. The structure and dynamical processes of winter synoptic-scale waves associated with cold surges over South America are documented in this paper. It is shown that the rotated extended empirical orthogonal function technique is capable of extracting well-defined regional patterns from 850-hPa meridional-wind perturbation fields. Over South America, waves behave very differently in the lower and middle troposphere: while upper-level waves propagate northeastward as they cross the Andes, ...