Cold air outbreaks, sometimes resulting in damaging frost, affect the
agricultural areas of southern and southeastern Brazil. At times, these occurrences have resulted in significant socio-economic impacts on the region and the country. Specific case studies have shown that strong cold air outbreaks are generally associated with a strongly amplified wave pattern in middle latitudes, with an amplified upper tropospheric ridge situated near or just to the west of the Andes mountains and a trough near the east coast of South America. The enhanced northward flow between the ridge and the trough
facilitates the rapid northward advance of cold air from Argentina to southern Brazil. In some cases, the primary front is reinforced by a secondary thrust of cold air that eventually results in the occurrence of frost at rather low latitudes. In this study, we focus on the interannual variability of cold air outbreaks and the synoptic conditions that accompany extreme cases leading to frost. Two analysed cases show differences in the upper level flow which caused
different conditions at the surface. The NCEP/NCAR reanalysis archive will be used for the analysis of the atmospheric circulation variables, and the extreme cases with frost are taken from previous studies. The sensitivity of the CPTEC/COLA model in predicting features related to frosts in south/southeast Brazil will be examined for selected extreme cases.