An Observing System Simulation Experiment (OSSE) was implemented to investigate the potential impact of the future MTG-IRS in the convective-scale AROME forecast system. In OSSE, simulated rather than real observations are the input to the 3DVar data assimilation system. Hence, all observation types (conventional and satellite measurements) as well as IRS radiances were simulated from the true state of the atmosphere: the Nature Run (NR). To make them more realistic, these values were explicitly increased by an appropriate amount of noise, sized on observation error. The resulting values were ingested into the data assimilation system, in the same way real observation would be in the operational system. Several configurations for the assimilation of water vapour MTG-IRS channels were evaluated as well as the CTL run in which all simulated observations are used except IRS.