The starting point of the NWP process is an accurate observation of the present weather and measurement of every variable linked to it: temperature, pressure, humidity, cloudiness, precipitation, wind intensit and direction, etc. Measurement of this kind of data is realized, on the surface, with the use, for example, of weather shelters, automatic meteorological stations, ships, and buoys; at heights, with weather balloons, recording information at different levels of altitude, satellites, radars, aircrafts, wind profilers, etc. It is clear then how important it is not just the rapidity with which the observed data arrive at the gathering centers, but also the fact that data are measured according to certain standard criteria, common to every station, to be able to compare the observations.
For the emanation of these criteria, the responsible is the World Meteorological Organisation (WMO), United Nations Agency promoting international cooperation in the observative meteorological field, through constant information exchange at the global level among participants countries through a modern telecommunication network reserved to meteorology. Observations, on national territory as well as in the rest of the world, are indeed realized in the context of the World Weather Watch (WWW) respecting Global Observing System (GOS) dictates, whose aim is to regulate and guarantee atmosphere state and oceanic surface observations to allow analysis, forecasts, warnings, for climate monitoring and environmental impact. Observed data and products derived from such measures, forecast included, are disseminated to the various meteorological centers via GTS (Global Telecommunication System, figure 2). Each nation is required to collect its own meteorological observation data for the transmission on telecommunication network of the GTS.
CNMCA/RESIA-GSIM in Pratica di Mare, as Regional Telecommunication Hub (RTH) for region VI – Europe, besides collecting data from the national territory, receives, for successive retransmission, data from Malta, Greece, Turkey, and Libanon and centralizes all data from European area. WMO Information System (WIS, (link is external)) represents the evolution of the GTS system for the WWW program, introducing a new meteorological centers classification as managing institutions of meteorological data and metadata catalogues (and not) that, as a whole, define the global Informative System of the WMO. In this context CNMCA/RESIA-GSIM conducts the dual function of Data Collection or Production Centre (DCPC), respectively in quality of RTH, already mentioned, and Regional Specialized Meteorological Centre (RSMC) for marine meteorology in the Mediterranean area.  Furthermore, CNMCA is equipped with systems for reception and processing of meteorological remote-sensed satellite data, both through direct reception in L and X band and through EUMETCAST network ( (link is external)) managed by Europe agency EUMETSAT.
It is important to underline that CNMCA, by virtue of recent bilateral agreements of the Italian Air Force with other Public Administrations and Private Institutions, receives even other high-density observations on its national territory, external to GTS circuit, and monitors their quality in view of operational use in the center data assimilation system.