What is already known:
What this study adds:
Dual threat severe weather events in which both tornadoes and flash floods affect the same area within a short time frame pose a complex problem since the life-saving actions for these two events are contradictory. One such event is the 6-7 May 2015 tornado and flash flood event over Oklahoma. This study explores the capability of a rapidly-updating 3-km horizontal grid spacing convective-scale ensemble data assimilation and prediction system developed as part of the Warn-on-Forecast initiative to forecast features of this dual threat severe weather event. Results indicate that the 0-1 h probabilistic forecasts of reflectivity verify reasonably well with the observations. However, beyond the 1 hour forecast period, the forecast accuracy is degraded, including biases in storm motion as well as spurious cell generation. The ensemble probability matched mean quantitative precipitation forecasts capture the placement of most intense areas of precipitation very well, but underestimate the amount of accumulated precipitation. These quantitative precipitation forecasts are found to outperform the deterministic quantitative precipitations forecasts of the operational High-Resolution Rapid Refresh model as well. Additional ensemble forecast experiments from simple downscaling to 1-km grid spacing from the 3-km ensemble do not significantly reduce the storm motion bias found in the original results and introduce more spurious cells.