Downscaled Ensemble Reforecasts of Extreme Rainfall Events

Since their advent, the meteorological forecast community has established the usefulness of ensemble-based numerical weather prediction (NWP) for precipitation forecasting. The reliance of operational forecasters on these systems for precipitation guidance has led to an increasing need to determine the most effective use of ensemble predication systems in high impact events, such as tropical cyclones. Recent efforts have led to development of global medium range ensemble reforecast datasets based upon operational NWP models, which provide a framework to investigate a variety of ensemble related research questions. This research will focus on using NOAA's Second Generation Global Medium-Range Ensemble Reforecast Dataset (Reforecast-2) to create downscaled ensemble reforecasts of tropical cyclones (TCs) and important features such as mesoscale convective vortexes (MCVs).

Specifically, the global reforecasts are used to force an ensemble of convection allowing WRF-ARW forecasts with the new WRF hydrologic modeling system (WRF-Hydro) coupled underneath. Some events examined during the course of this research are tropical storm Erin in 2007, the 2010 Arkansas MCV caused flood, and the flooding that occurred in San Antonio, TX in 2013. Ensemble analysis methods are used to diagnose atmospheric processes responsible for differences in the TC and MCV track and precipitation forecasts. Then, the way that these differences affect the hydrologic forecasts are examined to assess sensitivities in flood potential to particular atmospheric features. Any results will reflect the ability for downscaled ensemble NWP systems to represent previously unresolved mesoscale features, precipitation totals, and hydrologic responses.