Subseasonal Predictions with NCEP’s Unified Forecast System

NWS/NCEP, in collaboration with the larger research community, is developing a new coupled analysis and forecast system for sub-seasonal to seasonal scales within the Unified Forecast System (UFS) framework. This system will eventually replace the currently operational GEFS/CFSv2. The main components of the coupled UFS are: the atmospheric model with FV3 dynamic core from GFDL, MOM6 ocean model from GFDL, and CICE5 sea ice model from Los Alamos, all coupled through the National Unified Operational Prediction Capability (NUOPC) approach. Additions and upgrades to the forecast system planned in the near future include WAVEWATCH-III and a new physical parameterization package (CCPP) within FV3. As modeling components are switched or upgraded in the process of improving the system towards a final configuration, the UFS performance at sub-seasonal scales is tested and compared to earlier versions. This is done systematically at each significant upgrade, and is based on 168 35-day forecasts initialized on the 1^st and 15^th of the month between 1 April 2011 and 15 March 2018. Testing consists of assessment and comparison of various skill metrics for forecasts at weeks 1 through 5 for various fields such as SST, 2-m temperature, precipitation rate, OLR, 500mb heights, and others, both globally and at smaller domains of particular interest (e.g. continental US, Global Tropics, Nino3.4, and polar regions). This presentation will discuss the progress in the development of the UFS for sub-seasonal forecast through the latest upgrades in terms of these metrics versus the current operational model.