The Global Forecast System (GFS) is a global numerical weather prediction system containing a global computer model and variational analysis run by the U.S. National Weather Service (NWS).
The GFS is run four times a day, and produces forecasts for up to 16 days in advance. The forecast component uses the FV3 model with a resolution of ~13 km. In the vertical, the model is divided into 127 vertical layers. It produces forecast output every hour for the first 120 hours, then every 3 hours for days 5-16. Details on the June 2019 implementation of the initial FV3 version of the GFS (GFSv15) and the March 2021 implementation of GFSv16 can be found in the "Implementations" and "Documentation" links on the left side of this page.