Weather to subseasonal prediction from the UFS coupled Global Ensemble Forecast System

Abstract The current operational Global Ensemble Forecast System (GEFS) version 12 was implemented in National Centers for Environmental Prediction (NCEP) operations in September 2020. This is the first Unified Forecast System (UFS)-based GEFS which has demonstrated significant improvements in probabilistic forecast guidance at weather, medium-range and subseasonal scales based on the evaluation of 31-year reforecasts and 3-year retrospective forecasts. NOAA/NCEP is now planning to implement a fully coupled UFS Global Forecast System (GFS) and GEFS in 2025. Recently we have been working on the fully coupled GEFS versions following the development of UFS coupled model prototypes. Besides some updates from the model components like land model, ocean model and ice model, there are significant atmospheric model upgrades including increasing vertical resolution, PBL scheme, microphysics and gravity wave drag following the development of these model prototypes. In this paper, we present two coupled GEFS experiments that are based on UFS coupled model prototype 5 and 8 respectively. This paper aims to evaluate and compare the results from these coupled ensemble prototypes experiments as well as stochastic physics application, configuration and tuning progress in these coupled ensemble experiments for weather and subseasonal forecast. The results from those two coupled GEFS experiments show the improvements of the 500 hPa geopotential height probabilistic forecast skills (CRPSS) and model bias for all lead-time, the improvements of the precipitation forecast on the weather time scale of reliability and Hedike scale for weekly average including weeks 3&4, the skill-error ratios and MJO prediction as well.