The Global Forecast System (GFS) is a global numerical weather prediction system operated by the National Centers for Environmental Prediction (NCEP), part of the United States National Weather Service. It produces forecasts of atmospheric and land-surface conditions, including temperature, wind, precipitation, soil moisture, and atmospheric composition. The deterministic GFS forecast is run four times each day and covers out to 16 days in the future. The system also provides initial conditions and forecast information used by other National Weather Service prediction systems.
Operation The GFS is run four times each day, with forecasts initialized at 00:00, 06:00, 12:00, and 18:00 UTC. Each run produces forecasts for up to 16 days. The forecasts are initialized using analyses produced by the Global Data Assimilation System (GDAS). GDAS combines surface observations, weather-balloon measurements, aircraft reports, buoy observations, radar data, satellite observations, and other measurements within a three-dimensional representation of the atmosphere. As with other numerical weather prediction systems, forecast skill generally decreases as the forecast period increases because uncertainties in the initial conditions and approximations in the model grow with time. At longer ranges, forecasts are therefore more useful for identifying broad weather patterns than for predicting local conditions in detail.
Principles The operational GFS uses the Finite-Volume Cubed-Sphere Dynamical Core (FV3) with an approximate horizontal grid spacing of 13 km. The atmosphere is divided into 127 vertical layers extending from the surface to the mesopause, approximately 80 km above the surface. The GFS also includes a WAVEWATCH III wave-model component, coupled one-way so that the atmospheric model provides forcing to the wave model. The model's native grid should not be confused with the regular latitude–longitude grids on which forecast products are distributed. NCEP provides GFS output on several grids, including products with spacings of 0.25°, 0.5°, and 1.0°. Standard GFS forecast output is produced hourly through forecast hour 120 and at three-hour intervals thereafter through forecast hour 384. GFS output is also used in the production of model output statistics and other National Weather Service guidance products.
Variants NCEP also operates the Global Ensemble Forecast System (GEFS), an ensemble counterpart to the deterministic GFS. GEFS version 12 uses an approximately 25 km FV3 configuration and includes one unperturbed control forecast and 30 forecasts produced from perturbed initial conditions. It is run four times daily. The 06:00, 12:00, and 18:00 UTC runs extend to 16 days, while the 00:00 UTC run extends to 35 days. A separate GEFS-Aerosol forecast is run as a special member of the system. It produces forecasts of dust, sea salt, sulfate, and carbonaceous aerosols through 120 hours. The 31 atmospheric GEFS members are combined with 21 members from the Canadian Global Ensemble Prediction System to form the 52-member North American Ensemble Forecast System (NAEFS).
Usage NOAA distributes GFS analysis and forecast data through NCEP data servers and the NOAA Operational Model Archive and Distribution System (NOMADS). GFS data are also made available through commercial cloud infrastructure as part of the NOAA Open Data Dissemination program. Information produced by the National Weather Service and published on its government servers is generally in the public domain unless otherwise noted and may be reused without charge for lawful purposes. Users may not claim the information as their own, imply endorsement by NOAA or the National Weather Service, or present modified information as official government material. This availability allows outside organizations to incorporate GFS output into weather-forecast products and visualizations.
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