The basic statistics of aerological variables obtained from radiosonde data at Ezeiza, Buenos Aires, Argentina, for 1986 are examined, and their relationships with occurrence and non-occurrence of daily local precipitation are analysed. The resulting samples are statistically different for nearly all the variables. Nevertheless, thermodynamic variables at the 700 mb level and the K-Whiting instability index yield the best correlations with rainfall, though it is noted that they are diagnostic and not prognostic variables. 500 mb relative vorticity at selected gridpoints is included in the analysis, given the effectiveness of this dynamic field to recognise favourable patterns for daily precipitation occurrence. Some experiments using these potential predictors to specify occurrence or non-occurrence of the event within a 24-hour period are presented.