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 64 layers and temporally, 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 FV3 version of the GFS can be found in the "Implementations" link on the left side of this page.