Abstract. National Meteorological Services (NMSs) use different "classical" tools in order to diffuse meteorological information, including television, radio, newspaper, phone, e-mail and websites. In recent years, new communication technologies and, in particular, the rapid expansion of Facebook allows users to efficiently exchange information and to easily share it with a large part of the population.

Facebook is one of the most used social networks and it represents a perfect virtual platform to share information and to promote active and immediate interaction amongst users. This is why many NMSs develop new communication strategies and incorporate this tool for different purposes. Some NMSs not only provide forecast, real-time observed data and other routine information, but they also upload videos (for example, with the weatherperson explaining the forecast or short reports) and amazing pictures taken by followers. In addition, they also give educational and didactic information (above all about climatic issues) and organize photographic competitions.

In this paper, firstly, we investigate when Facebook was introduced in different NMSs worldwide as an additional tool for the diffusion of meteorological information. Then, we propose a classification of these NMSs based on the success of their Facebook page, i.e. on the number of followers. Finally, we select some representative cases of NMSs and we analyze how Facebook is used to improve their services.