The Development of the NCEP Global Ensemble Forecast System Version 12

Abstract The Global Ensemble Forecast System (GEFS) is upgraded to version 12, in which the legacy Spectral Model (GSM) replaced by a model with new dynamical core—the Finite Volume Cubed-Sphere Dynamical Core (FV3). Extensive tests were performed determine optimal and ensemble configuration. GEFS has cubed-sphere grids horizontal resolution of about 25 km an increased size from 20 30. It extends forecast length 16 35 days support subseasonal forecasts. stochastic total tendency perturbation (STTP) scheme two uncertainty schemes: stochastically perturbed physics tendencies (SPPT) kinetic energy backscatter (SKEB) scheme. verification on period more than years retrospective runs. results show that outperforms operational-at-the-time all measures included package. system better error–spread relationship, significantly improved skills large-scale environment forecasts, precipitation probability forecasts over CONUS, tropical cyclone track intensity reduced 2-m temperature biases North America. GEFSv12 was implemented 23 September 2020.