The mathematical model is run four times a day, and produces forecasts for up to 16 days in advance, but with decreased spatial resolution after 10 days. The forecast skill generally decreases with time (as with any numerical weather prediction model) and for longer term forecasts, only the larger scales retain significant accuracy. It is one of the predominant synoptic scale medium-range models in general use.
The GFS model is a spectral model with an approximate horizontal resolution of 13km for the first 10 days and 27km from 240 to 384 hours (16 days). In the vertical, the model is divided into 64 layers and temporally, it produces forecast output every hour for the first 12 hours, three hourly through day 10 and 12 hourly through day 16. More information on the upgrade to 13km (T1534) can be found: http://www.emc.ncep.noaa.gov/GFS/impl.php. The output from the GFS is also used to produce model output statistics.
In addition to the main model, the GFS is also the basis of a lower resolution 20-member (22, counting the control and operational members) ensemble that runs concurrent with the operational GFS and is available on the same time scales. This ensemble is referred to as the "Global Ensemble Forecast System" (GEFS). Ensemble model output statistics are also available out to 16 days. The GFS ensemble is combined with Canada's Global Environmental Multiscale Model ensemble to form the North American Ensemble Forecast System (NAEFS).
As with most works of the U.S. government, GFS data is not copyrighted and is available for free in the public domain under provisions of U.S. law. Because of this, the model serves as the basis for the forecasts of numerous private, commercial and foreign weather companies.