The present work analyzes the monthly precipitation data at Buenos Aires Station – Central Observatory Station. The hypothesis is that rainfall is compound by two classes of contributions: precipitation coming from convective cloudiness on the one hand and non-showery or stratus clouds on the other. Occasionally they can be together, and others one of them can appear alone. The main objective is to separate these two different rainfall classes of the rainfall using the hourly rainfall information obtained from pluviograph registers and the hourly present time reports, corresponding to January 2002 – December 2012 by the mentioned station. In order to establish the category “convective precipitation amount”, the hourly present time records asociated with convective phenomena (according to SYNOP code) was estracted from the hourly present time data. The hourly rainfall was determined by direct reading of the pluviographic bands. Then, the hourly present time reports were linked with the days and the hours of the rainfall data. That way when one given hour had rainfall record and had a convective hourly time present report too, this accumulated hourly rainfall was classified as convective precipitation. Therefore, the remaining rainfall reports were classified as stratiform precipitation. Hence, the analysis shows a bigger contribution to the convective precipitation from the month of October to March, which has a bigger variability.