The objective of the project was to build a real-time system and service for forecasting potential evapotranspiration for Poland, known also as EvapProg, with a particular emphasis put on a basin-scale analysis. The focus on catchments is particularly important as the system is mainly targeted at modelers who build and run hydrological models. The system integrates three data sources that are available in real time: numerical weather predictions from the Weather Research and Forecasting (WRF) mesoscale meteorological model, the Leaf Area Index (LAI) estimates from satellite-based Moderate Resolution Imaging Spectroradiometer (MODIS), and snow extent daily maps obtained from the satellite, namely using Special Sensor Microwave Imager/Sounder (SSMIS). The EvapProg system produces prognoses of potential evapotranspiration for the entire Poland using the Penman-Monteith equation, with lead time of 2 days and 6-hour sampling. The forecasts are available in a WRF-based web map service (meteo.plgrid.pl), however, the key added value offered by EvapProg is the basin-scale prognosis of potential evapotranspiration which is available as a query and hence may be embedded into the code of hydrological models that work operationally in real time.