Storm-scale Data Assimilation and Ensemble Forecasts of the 31 May 2013 Oklahoma Tornado and Flash Flood Event

A multiscale ensemble data assimilation and prediction system using the WRF-ARW model and the Data Assimilation Research Testbed (DART) software is developed at National Severe Storms Laboratory as part of the National Oceanic and Atmospheric Administration's Warn-on-Forecast (WoF) initiative. To evaluate the capabilities of this WoF type system in producing storm-scale short-range probabilistic forecasts of hazardous weather events, the 31 May 2013 tornado and flash flood event over central Oklahoma (OK) is chosen. The initial and boundary conditions for the 36-member multiphysics meso- and storm-scale ensemble are obtained from the Global Ensemble Forecast System (GEFS) at 0000 UTC 31 May. Routinely available observations are assimilated on an hourly basis on both grids for more than a day. Before the onset of the evening tornado and flash flood hazard, observations from four operational WSR-88Ds and conventional platforms are assimilated continuously every 5 min into the storm-scale ensemble for the entire event period and 6-h ensemble forecasts are launched from the analyses every 30 minutes. The probabilistic forecasts of the reflectivity and low level mesocyclones of the El-Reno, OK tornadic supercell storms and the probabilistic quantitative precipitation forecasts (PQPF) for the later flash flood event over central OK from this continuously cycled system will be presented at the conference.