NCEP GEFS V11 Reforecast and its Application

The Global Ensemble Forecast System (GEFS) version 11 (v11) was implemented on 2nd December 2015 at the National Centers for Environmental Prediction (NCEP). Afterward the NCEP Environmental Modeling Center (EMC) generated a 20-year GEFS reforecast for the upgrade version. The reforecast includes 5-member initialized every 4-day at 00UTC. The control initial conditions were generated by the Climate Forecast System Reanalysis (CFSR) and Grid-point Statistical Interpolation (GSI) system for the period of 1996-2010 and 2011-2015, respectively. The similar forecast outputs like GEFS production are available for various applications.

The major changes of GEFS v11 include the latest Global Forecast System (GFS) model which changes from Euler integration of advection to semi-Lagrangian method, using EnKF 6hr forecast as initial perturbations instead of BV-ETR, increasing model resolution from T254L42 to TL574L64 for day 0-8, from T190L42 to TL382L64 for day 8-16, and model output frequency et al.  The overall evaluation of GEFSv11 from 2-year full retrospective runs and 20 years reforecasts is much better than GEFSv10. For example, NH 500hPa height has extended forecast skills (60% AC) by 8 hours and hurricane track forecast error for 72 hours has reduced by 10% for all basins.  In this study, we will focus on the spatial-temporal distributions of the bias and evolution during model integration. In particular, we have found GEFSv11 has an increased warm 2-meter temperature bias for warm season and a decreased 2-meter temperature cold bias for cold season. The reforecast climatology and model bias have been generated those will be applied to the bias correction, extreme weather forecast and et al. These results will be presented.