The Transition of Global Ensemble Forecast System to Fully Coupled Earth System Model for Subseasonal Predictions

The Unified Forecast System (UFS) based Global Ensemble Forecast System version 12 (GEFS v12) will be implemented in NCEP operations in September 2020. This upgraded GEFS has demonstrated a great improvement of the probabilistic forecast guidance for weather, medium range and subseasonal predictions based on 31-year reforecasts and 3-year retrospective forecasts. The GEFS v12 will run 31 members, at 25km horizontal resolution, out to 35 days compared to the current 21 members, 33 km horizontal resolution and out to 16 days respectively. The GEFS v12 system has also included wave and atmospheric aerosol components with this upgrade.

This talk will mainly focus on forecast uncertainties of subseasonal predictions and plans for the transition from uncoupled GEFS v12 to fully coupled GEFS v13. The presentation will cover the following three aspects: 1). The success and highlights of GEFS v12 for weather and subseasonal predictions through various evaluation metrics; 2). The discussion of challenges associated with the un-coupled ensemble system, especially for subseasonal predictions; 3). Expectations from a fully coupled global ensemble forecast system toward next operational implementation.