The coupled National Water Model (NWM)–Height Above Nearest Drainage flood mapping methodology provides the basis for operational flood forecasting across the continental United States. This paper evaluates how the method performs for 28 case studies using a historic archive of flood extents and a retrospective run of the NWM. We provide a summary of the results and discuss where the method is performing reliably, the general reasons for poor forecasts, and how the method might be improved.