The purpose of this study was to verify the relationship between the potential energy Convective Available (CAPE) and the precipitation over the eastern Amazon, in order to discuss and evaluate the importance of thermodynamic and dynamic factors associated with the type of occurred cloudiness. For this, using two different methods, was made the thermodynamic classification of radiosondes released during the CHUVA Project experiment (Cloud processes of tHe main precipitation systems in Brazil: The contribution to cloud resolving modeling and to the GPM (Global Precipitation Measurement), in the cities of Belem, São Miguel do Guama and Tome-Açu, northeastern state of Para. The release period of radiosondes was of 19 to 26 June 2011, daily in the times of 03:00, 09:00, 15:00 and 21:00 Local Hour (HL). Rainfall data were collected from surface automatic weather stations of National Institute of Meteorology (INMET) in the cities of Belem, Castanhal, Soure and Tome-Açu, in addition of data collected from a homemade rain gauge in Marituba and weather information of METAR code from Belem International Airport. The images of weather satellite GOES-12 and S-band weather radar, located in Belem, also assisted in the verification of rainfall during the project period. The thermodynamic classification of radiosondes, showed that the atmosphere in the region presented, alternating between stability and instability situations, related with the acting of meso scale systems associated at thermodynamic factors, which contributed to the occurrence of rain. The rains usually occurred in periods of the afternoon and in the evening. The CAPE almost always presented high values, and also a well-defined diurnal cycle, with maximum and minimum values occurring at 15:00 and 03:00, respectively, however, this cycle was broken every time that occurred precipitation. The interaction between the thermodynamic and dynamic forcings had quite contribution to the formation of rainfall that occurred in the region during the project, being in this case, the acting of sea breeze in the region which increased instability associated with high values of CAPE in the three cities
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