A real-time flood forecasting system was developed over the Klzlllrmak river basin (KRB) in Turkey by means of a physically-based atmospheric-hydrological model. The real-time flood forecasting system utilizes the weather research and forecasting (WRF) model and the WRF data assimilation (WRFDA) system as its atmospheric component. Real-time global atmospheric forecasting data are obtained from global forecast system (GFS) operated by the national centers for environmental prediction (NCEP). The real-time global atmospheric forecasting data are utilized as initial and boundary conditions of the atmospheric component. The atmospheric component synthesizes real-time upper-air sounding data and ground observations into the initial conditions by the three-dimensional variational (3DVAR) data assimilation system. After the assimilation, the atmospheric component dynamically downscales the real-time global atmospheric forecasting data into 4 km horizontal resolution and hourly temporal resolution. The real-time flood forecasting system is in operation now. Some preliminary forecasted results by the atmospheric component are shown in this presentation.