The Experimental Regional Ensemble Forecast System (ExREF)
The ExREF domain covers most of North America and has 9-km horizontal grid spacing. The ensemble has eight members, all employing WRF-ARW. The ensemble uses a variety of initial conditions from Local Analysis and Prediction System (LAPS) analyses and the Global Forecasting System (GFS) together with multiple boundary conditions from the GFS ensemble. Additionally, a diversity of physical parameterizations is used to increase ensemble spread and to account for the uncertainty in forecasting extreme precipitation events.
ExREF has been a component of the Hydrometeorology Testbed (HMT) NWP suite in the 2012-2013 winter. ExREF ensemble means for a subset of parameters and geographic coverage are distributed to the National Weather Service (NWS) Weather Forecast Office and the California Nevada River Forecast Center in Sacramento, where they are ingested in the Advanced Weather Interactive Processing System (AWIPS I and AWIPS II respectively) to provide guidance on the forecasting of extreme precipitation events. ExREF is also being supplied to the NWS NCEP Weather Prediction Center where it was tested in the 2013 Flash Flood and Intense Rainfall Experiment. Finally, ExREF is being used at NOAA/ESRL/GSD as a proving ground for new methodologies in ensemble forecasting. An alternative initialization technique, termed dynamic downscaling of perturbations is being implemented and will be evaluated by the Developmental Testbed Center (DTC) for potential operational implementation in the NWS operational Short Range Forecasting System (SREF).