This paper presents a classification of atmospheric circulation fields in surface and 500 hPa over South America during the month of December, in order to identify the main synoptic patterns that influence the weather in the Southeast region of Brazil, especially in the state of Minas Gerais (MG). To this purpose, the Rotated Principal Component Analysis technique was applied to the NCEP reanalysis for the period 1986-2011. The principal aim of this classification was to determine the circulation patterns prevailing during the month of December 2011 related to the anomalous rainfall occurred in the State of Minas Gerais (MG). The results provide six circulation patterns in surface and four circulation patterns in altitude that are representative of about 72.8% and 94% of all the cases, respectively. Three main surface circulation patterns associated with higher probability of precipitation over the State of MG were found. One of them was associated with the advance of a cold front that reaches the southern part of the Southeast region of Brazil (PSP2-Sup), and two others (PSP3-Sup and PSP5-Sup) related to a "dipole" blocking configuration over Atlantic ocean determined by an anticyclone located around 50 º W, 45 º S and a low positioned north of the anticyclone around 25 º S. At 500 hPa two main circulation patterns were associated with the occurrence of significant precipitation over the State of MG reflecting the low level circulation; one associated with a cold front (PSP2-500) and another related to a "dipole" blocking situation over the Atlantic Ocean (PSP4-500). The anomalous rainfall observed during December 2011 were associated directly with the PSP3-Sup and PSP4-500 and both of them were related to the performance of South Atlantic Convergence Zone (SACZ) episodes.
synoptic clasification; principal components; anomalous rainfall
