Amending Numerical Weather Prediction forecasts using GPS Integrated Water Vapour: a case study

With GPS independent observations of
humidity can be made. The data quality has shown to be
very good and the high temporal resolution can be of
great value for forecasters. GPS Integrated Water Vapour (IWV) can be used to validate the amounts of humidity in Numerical Weather Prediction (NWP) model forecasts. This paper presents a case in which the operational limited area model at KNMI (as well as the global model of ECMWF) strongly underestimated the diurnal temperature cycle. The humidity in the boundary layer of the model triggered evaporation, which affected the temperature forecast. Goal of this paper is to show the additional information of GPS IWV for NWP models and discuss the benefit and use of the GPS IWV observations for amending the operational forecast.