The Experimental Regional Ensemble Forecast System (ExREF)

The Experimental Regional Ensemble Forecast (ExREF) system is a tool for developing and testing new Numerical Weather Prediction methodologies. ExREF is a joint project between the Global Systems Division (GSD) of the NOAA Earth System Research Laboratory (ESRL), the Hydrometeorological Testbed (HMT), the Environmental Modeling Center (EMC), and the Weather Prediction Center (WPC) of the National Centers for Environmental Prediction (NCEP), among other partners.

The ExREF domain covers most of North America and has a 9-km horizontal grid spacing. Currently the ensemble has eight members, all using different versions of the WRF-ARW model. The ensemble is initialized with a variety of initial conditions from the Global Forecasting System (GFS) and GSD's Local Analysis and Prediction System (LAPS) and uses multiple boundary conditions from the operational GFS ensemble. Additionally, a variety of physical parameterization schemes is used to increase ensemble diversity with an aim to capture extreme precipitation and other high impact weather events.

ExREF is run in near-real time by GSD and products are made available to the user community through a variety of channels such as a website, an FTP site, the Unidata Local Data Manager, GSD's Thematic Realtime Environmental Distributed Data Services (THREDDS), and for selected users, direct access from the native computing platform. Near-real time execution of ExREF gives forecasters an opportunity to use and test new technologies, while GSD receives detailed user feedback, closing the developer-user loop. For example, in the winter of 2012 - 2013, ExREF was used in HMT activities in which products were distributed to the National Weather Service Western Region Weather Forecast Offices and the California Nevada River Forecast Center in Sacramento. Guidance on extreme precipitation events was displayed on the Advanced Weather Interactive Processing System I and II (AWIPS). At the WPC, ExREF 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, called dynamic downscaling of perturbations, is being implemented and will be evaluated by the Developmental Testbed Center for potential Research to Operations transition to the NCEP operational Short Range Forecasting System (SREF).

The improvement of operational numerical models relies on robust technology transfer practices. At GSD, we strive to develop new systems through collaboration between NOAA scientists and the scientific community. ExREF provides a framework for this collaboration to take place and for new techniques to be tested. Through close coordination with the EMC, advancements in ExREF can directly be transferred to the models that provide daily guidance to the nation's forecasters.

Contact information
Name: Zoltan Toth
Tel: 303-497-5042