Assimilation of the water vapour in the mesoscale Numerical Weather Prediction (NWP) models has been an objective in the last decade. As the radiosondes does not provide good temporal and spatial coverage needed by the fine resolution mesoscale models the Integrated Water Vapour (IWV) information is retrieved from the Global Positioning System (GPS) delays. Since July 2001 a nonhydrostatic mesoscale model called aLpine Model (aLMo) has been used for operational NWP in MeteoSwiss. The GPS data provided for the Near Real Time Campaign of the COST Action 716 "Exploitation of ground based GPS for climate and numerical weather prediction application" have been assimilated in aLMo with the nudging technique. On average 110 GPS sites from Europe have been selected for the assimilation experiments in three different weather regimes namely, advective period in September 2001, summer convection - June 2002 and winter stratus - January 2002. The results from the model analysis and forecast runs are analysed to access the impact of the GPS-derived IWV on the model performance with respect to the precipitation and the cloud cover forecast.