The Development of the Next-Generation NCEP Global Ensemble Forecast System (GEFS)

The Next Generation Global Prediction System (NGGPS) initiative, started in 2015, has led to an envisioned community-based Unified Forecast System (UFS) that will have a National Weather Service (NWS) operational model running at the National Centers for Environmental Prediction (NCEP). As the first operational part of the UFS, the deterministic Global Forecast System (GFS) will be upgraded in early 2019 and the corresponding ensemble system, the NCEP Global Ensemble Forecast System (GEFS) will be upgraded from the current operation version (v11) to a new version (v12) later in 2019.

In contrast to the operational GEFS (v11), GEFS v12 will be significantly changed in the following ways: 1). The dynamic core will be switched from spectral to Finite-Volume Cubed-Sphere (FV3) representation; 2). Model horizontal resolution will be increased from 34 km (0-8 days), and 55 km (8-16 days) to 25 km (0-16 days); 3). GFDL microphysics scheme will replace the currently-operational Zhao-Carr scheme; 4). Forecast leength will be extended from 16 to 35 days to cover subseasonal prediction. In addition, scientific enhancements include new stochastic schemes (SKEB, SPPT and SHUM – replacing STTP), a so-called 2-tiered representation of SSTs, and a scale-aware convection parameterization, all of which enhance prediction skills in the weeks 3&4 time period. The GEFS v12 implementation package includes a 20-year reanalysis and 30-year reforecast to calibrate the ensemble forecast, a summary of which will be submitted in a separate abstract.

GEFS v13 is under development, with a particular focus on three areas: 1). A fully coupled atmosphere-land-ocean-ice-wave-aerosol system that will support weather, week-2 and subseasonal forecast; 2). Process based stochastic parameterization that will help improve forecast uncertainties including near-surface; 3). Advanced model physics, which includes an updated convection scheme, that will enhance the prediction of tropical convection and MJO propagation.