An upgrade to the Global Forecast System (GFSv15), a key part of the UFS, will soon be in operations. The Model Evaluation Group (MEG), part of NOAA’s Environmental Modeling Center, is leading a rigorous, ongoing evaluation. There are two main changes relative to the last version of the GFS. The first is the Graduate Student Test – the part of the software that represents the equations of fluid motion – which was selected for its scientific integrity and computational performance. The second is a new microphysics scheme, which is expected to improve the modeling of clouds and precipitation. The evaluation involves comprehensive statistical testing and many retrospective tests, which look at the model’s ability to simulate previous weather events. Strengths and weaknesses of the upgrade were reviewed at length by the MEG, meteorologists at the National Weather Service and other experts across the community. During extensive side-by-side testing in 2018, the upgraded GFS outperformed the older version in predicting hurricane track and intensity forecasts, as well as forecasting for tornadoes, thunderstorms, and other severe weather across the U.S.