A prototype hydrometeorological model for real-time, site-specific, flash flood prediction is presented. Precipitation prediction components are coupled with runoff-generating and flood-routing components through the water mass conservation law and a state estimator which was used for updating the model state variables from real-time observations. The model is capable of operating under the various data availability conditions existing in flash flood prone areas. Sensitivity analysis using data from significant past flash floods indicates that short-term model predictions are not significantly sensitive to the runoff-generating model component when updating is performed. In addition, the sensitivity analysis suggested that model performance is best when all available meteorological and hydrological data are utilized by the state estimator. Remarkably (given the data available for calibration) good predictions of stream stage were obtained by the model for several flash flood cases.