A coupled atmospheric-hydrological model (CAHM) with a high-resolution, self-nesting and one-way coupling capability is employed to simulate the severe rainfall event that lead to a flood in May 2000 over southern Ontario. Three verification approaches are carried out to evaluate the atmospheric mesoscale model performance. The results show that the 48-h accumulated peak precipitation simulated by a mesoscale model successfully captures the observed peak rainfall recorded over a spatially dense rain gauge network in southern Ontario. Furthermore, the quantitative evaluation of the model predicted precipitation demonstrates that there is a systematic improvement in terms of the accuracies and skills when the model resolution is increased. In addition, an independent verification by comparing the CAHM simulated streamflow with the observed hourly streamflow shows the excellent agreement between the simulations and the observations in terms of magnitudes and timing of peak streamflows, indicating that precipitation is well simulated by the atmospheric mesoscale model.