In the field of summer cooling by ventilation and/or evaporation, a good knowledge of the dry and wet bulb temperatures represents the basis of any simulation processes. The summer of the city of Geneva was analysed based on extracted from a large amount of climatic data obtained in downtown and its surroundings. The data study over the three summer months of the last decade shows that if the climate varies only very little from one summer to the other, there is nevertheless a considerable difference according to whether one is in urban or rural zones. In addition, summer 2003 is far apart from the average statistics. This study aims to establish a representative database on average summer temperature conditions, downtown and in rural sites, as well as extreme conditions like in summer 2003. A comparative study is also made with the Meteonorm software, which is the commonly used tool to generate data when no station is available.