The National Centers for Environmental Prediction (NCEP/NOAA) will upgrade its Global Forecast System (GFS) to version 16 in February 2021. Development of the GFSv16 started one and a half years ago, building upon the implementation of version 15, which featured a new FV3 atmospheric model dynamic core, in June 2019. This talk will present several upgrades included in GFSv16, their impact on downstream applications, and testing and evaluation results from pre-implementation real-time and retrospective parallel experiments. GFSv16 is an implementation of the Unified Forecast System (UFS) featuring an increase in the number of model vertical layers from 64 to 127, whereas the model top is extended from the upper stratosphere to the mesopause (~80 km height). Major upgrades in model physics include: (1) employing a new scheme to parameterize sub-grid scale stationary and non-stationary gravity waves; (2) adopting a scale-aware TKE-EDMF scheme to better represent the PBL processes; and (3) updating the RRTMG radiation package. Major changes in data assimilation include: (1) spinning up an offline land model with observed precipitation to provide improved land initial conditions, (2) using LETKF with model space localization and linearized observation operator to replace the Ensemble Square Root Filter, (3) employing the 4-Dimensional Incremental Analysis Update technique, (4) adopting SKEB perturbation technique in the ensemble forecast component, updating variational quality control, applying Hilbert curve to aircraft data, and inter-channel correlated observation error for CrIS and IASI observations, and (5) assimilating new satellite observations. In addition, GFSv16 includes a one-way coupled wave component that will replace the current operational stand-alone global deterministic wave model.
