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An example of a forecast product from the GFS, in this case a 96-hour forecast of 850 mb geopotential height and temperature

The Global Forecast System (GFS) is a global numerical weather prediction system containing a global computer model and variational analysis run by the United States' National Weather Service (NWS).

Operation

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.[1] 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.

Principles

The GFS model has a finite volume cubed sphere (FV3) dynamical core with an approximate horizontal resolution of 28 km between grid points, which drops to 70 km between grid points for forecasts between one and two weeks. In the vertical, the model is divided into 127 layers and extends to the mesopause (roughly ~80 km). It produces forecast output every hour for the first 120 hours,[2] three hourly through day 10, and 12 hourly through day 16. The output from the GFS is also used to produce model output statistics.

Variants

In addition to the main model, GFS is also the basis for a lower-resolution ensemble, the Global Ensemble Forecast System (GEFS), which runs 31 members (30 perturbed members plus a control member) alongside a 32nd, aerosol-only member run out to 5 days.[3] The GFS ensemble is combined with Canada's Global Environmental Multiscale Model ensemble to form the North American Ensemble Forecast System (NAEFS).

Usage

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.[4] Because of this, the model serves as the basis for the forecasts of numerous private, commercial, and foreign weather companies.

Accuracy

By 2015, the GFS model had fallen behind the accuracy of other global weather models.[5][6] This was most notable in the GFS model incorrectly predicting Hurricane Sandy turning out to sea until four days before landfall, while the European Centre for Medium-Range Weather Forecasts' model predicted landfall correctly at 7 days. Much of this was suggested to be due to limits in computational resources within the National Weather Service. In response, the NWS purchased new supercomputers, increasing processing power from 776 teraflops to 5.78 petaflops.[7][8][9]

As of the 12z run on 19 July 2017, the GFS model has been upgraded. Unlike the recently upgraded ECMWF, the new GFS behaves a bit differently in the tropics and in other regions compared to the previous version.[10] This version accounts more accurately for variables such as the Madden–Julian oscillation and the Saharan Air Layer.

In 2018, the processing power was increased again to 8.4 petaflops,[11] The agency also tested a potential replacement model with different mechanics, the flow-following, finite-volume icosahedral model (FIM), in the early 2010s; it abandoned that model around 2016, after it did not show substantial improvement over the GFS.

NOAA has continued to upgrade the GFS since, most substantially with the version 16 upgrade in March 2021 (see Development history below). This left some meteorologists hopeful it would be enough to close the accuracy gap with the ECMWF's model, then considered the most accurate global weather model.[12][13]

Independent verification has generally continued to find ECMWF's model more accurate than GFS in the medium range (three to seven days) even after the version 16 upgrade, a gap attributed to ECMWF's higher resolution and larger ensemble.[14] NCEP publishes ongoing comparative verification scores for GFS against ECMWF and other models.[15]

In March 2025, the NWS reduced or suspended twice-daily radiosonde ("weather balloon") launches at numerous upper-air stations nationwide, citing staffing shortages following federal layoffs. Several meteorologists warned that the resulting loss of upper-atmosphere observational data could degrade GFS and GDAS forecast accuracy, while the NWS stated it had seen no evidence that forecasts had been degraded.[16][17]

Development history

Transition to the FV3 dynamical core

After several years of testing, NOAA upgraded the GFS with a new dynamical core on June 12, 2019: the GFDL Finite-Volume Cubed-Sphere Dynamical Core (FV3), which uses the finite volume method instead of the spectral method used by earlier versions of the GFS. The resulting model, initially developed under the name FV3GFS, inherited the GFS moniker, with the legacy GFS continuing to be run until September 2019.[18][19] Initial testing of the FV3-based GFS showed promise, improving upon the large-scale prediction skill and hurricane track accuracy of the legacy GFS.[20]

Recent and planned upgrades

With the initial operational implementation of FV3GFS accomplished, NCEP's Environmental Modeling Center (EMC) upgraded the model to GFS version 16 on 22 March 2021, doubling the number of vertical layers from 64 to 127, extending the model top from the stratosphere to the mesopause, and adding new physics and data assimilation schemes.[21]

GEFS was separately upgraded to version 12 on 23 September 2020, marking the first global application of the Unified Forecast System (UFS) community model in an ensemble.[3] This upgrade:

  • Adopted the FV3 dynamical core as GEFS's atmospheric component, matching GFS v15
  • Increased horizontal resolution to approximately 25 km
  • Extended forecast length from 10 to 16 days (35 days for the 0000 UTC cycle)
  • Increased ensemble size from 21 to 31 members
  • Coupled the atmospheric ensemble to the NCEP Global Wave Model
  • Added a 32nd, unperturbed member ("GEFS-Aerosol") run to 5 days for aerosol prediction, based on GOCART/GSD-Chem

This was NCEP's first global-scale coupled ensemble system, replacing the previous standalone Global Wave Ensemble and NEMS GFS Aerosol Component (NGAC) systems. More details can be found at the EMC Model Evaluation Group's GEFS v12 web site, the EMC GEFS web page, and the EMC GEFS-Aerosol web page.

Subsequent point releases kept GFS within the version-16 line, including v16.3.0 in November 2022 (aviation and snow-depth improvements)[22] and further maintenance updates through 2024–2025 addressing satellite data ingestion and other observational systems.[23] NCEP proposed a further GFS v16.4.0 upgrade in April 2025, covering GDAS changes including new WindBorne balloon and saildrone observations and additional satellite radiance assimilation.[24]

NCEP introduced a new suite of AI-driven global models alongside the traditional GFS/GEFS on 17 December 2025: the Artificial Intelligence Global Forecast System (AIGFS), the Artificial Intelligence Global Ensemble Forecast System (AIGEFS), and the Hybrid Global Ensemble Forecast System (HGEFS).[25] AIGFS and AIGEFS are based on a version of Google DeepMind's GraphCast model fine-tuned using NCEP's Global Data Assimilation System (GDAS) analyses; AIGEFS is a 31-member AI ensemble, and HGEFS combines it with the physics-based GEFS v12 into a 62-member "grand ensemble." NOAA reported that the AI models achieve forecast skill comparable to or exceeding the traditional systems — AIGEFS extends forecast skill by an estimated 18 to 24 hours beyond the operational GEFS — while using only a small fraction of the computing resources required by the physics-based models.[26] The deployment is part of a broader shift toward operational machine-learning forecasting, with comparable AI systems now run by other national weather agencies, including Germany's DWD (AICON) and Canada's ECCC (GEML).[27] A March 2026 rapid-response report by NOAA's Science Advisory Board Environmental Information Services Working Group (EISWG), an external advisory panel, found the AI-based systems performed comparably to the traditional models on standard metrics such as 500 hPa anomaly correlation, but noted weaker performance for surface precipitation and for tropical and extratropical cyclone intensity.[28]

As of early 2026, EMC has proposed separating aerosol forecasting from GEFS entirely, replacing the GEFS-Aerosol component with a standalone Global Chemistry and Aerosol Forecast System (GCAFS) version 1.0 coupled to a new Global Constituent Data Assimilation System (GCDAS).[29]

Separately, EMC has since 2020 been developing a more fundamental successor to the version-16 line under the UFS Research-to-Operations (UFS-R2O) project: a fully coupled atmosphere–ocean–sea ice–wave–aerosol system built under the UFS framework, designated GFS version 17 and its ensemble counterpart GEFS version 13.[30] This next-generation system adds ocean (MOM6), sea ice (CICE6), and aerosol (GOCART) components to the existing atmosphere–wave coupling, increases horizontal resolution to approximately 9 km, and is intended to be the first coupled global application to run operationally under the UFS.[31] On 15 April 2026, NWS formally proposed the GFS v17 upgrade for operational implementation around October 2026; as of the proposal, no final Service Change Notice confirming an implementation date had been issued.[32]

See also

References

  1. ↑ "GFS". NOAA/NWS Environmental Modeling Center. Retrieved 2 August 2026.
  2. ↑ Timothy McClung. "Technical Implementation Notice 16-11 Amended". Nation Weather Service. Archived from the original on 5 June 2016. Retrieved 5 June 2016.
  3. 1 2 "NOAA upgrades Global Ensemble Forecast System". National Oceanic and Atmospheric Administration. September 2020. Retrieved 2 August 2026.
  4. ↑ "Disclaimer". National Weather Service. Retrieved 2 August 2026.
  5. ↑ Berger, Eric (21 June 2016). "The US weather model is now the third-fourth best in the world". Ars Technica.
  6. ↑ Berger, Eric (11 March 2016). "The European forecast model already kicking America's butt just improved". Ars Technica. Retrieved 16 August 2016.
  7. ↑ Kravets, David (5 January 2015). "National Weather Service will boost its supercomputing capacity tenfold". Ars Technica. Retrieved 16 August 2016.
  8. ↑ Rice, Doyle (22 February 2016). "Supercomputer quietly puts U.S. weather resources back on top". USA Today. Retrieved 16 August 2016.
  9. ↑ "NOAA completes weather and climate supercomputer upgrades". NOAA. Retrieved 16 August 2016.
  10. ↑ Team, NCO Web. "NCO PMB – Upcoming Changes". www.nco.ncep.noaa.gov. Retrieved 19 July 2017.
  11. ↑ "NOAA kicks off 2018 with massive supercomputer upgrade | National Oceanic and Atmospheric Administration". www.noaa.gov. 9 January 2018. Retrieved 20 August 2018.
  12. ↑ Lauren Gaches (22 March 2021). "NOAA upgrades flagship U.S. global weather model". NOAA. Retrieved 14 September 2021.
  13. ↑ Paul Douglas (18 April 2021). "Will a New GFS Weather Model Upgrade Close the Gap with The European Model?". AerisWeather. Retrieved 14 September 2021.
  14. ↑ "Comparative evaluation of ECMWF and GFS for operational day-ahead wind speed forecasting". Energy Conversion and Management X. 2026. Retrieved 2 August 2026.
  15. ↑ "GFS Verification". NCEP/EMC. Retrieved 2 August 2026.
  16. ↑ "The National Weather Service Is Slashing Critical Data Balloon Launches Due to Staffing Shortages". NOTUS. 20 March 2025. Retrieved 2 August 2026.
  17. ↑ "Is missing weather balloon data making forecasts worse?". Capital Weather. July 2026. Retrieved 2 August 2026.
  18. ↑ "Service Change Notice 19-40" (PDF). NOAA. Retrieved 12 June 2019.
  19. ↑ "NOAA to develop new global weather model | National Oceanic and Atmospheric Administration". 27 July 2016.
  20. ↑ "NOAA Budget Cuts Get Chilly Reception in Congress". 27 April 2018.
  21. ↑ "Service Change Notice 21-20: Upgrade NCEP Global Forecast Systems (GFS) to v16" (PDF). National Weather Service. 18 March 2021. Retrieved 2 August 2026.
  22. ↑ "Service Change Notice 22-104: Upgrade NCEP Global Forecast System to v16.3.0" (PDF). National Weather Service. 2 November 2022. Retrieved 2 August 2026.
  23. ↑ "Service Change Notice 24-65: Upgrade NCEP Global Forecast System to v16.3.16" (PDF). National Weather Service. 14 June 2024. Retrieved 2 August 2026.
  24. ↑ "Public Information Statement 25-23: Soliciting Comments on the Proposed Upgrade of the Global Forecast System (GFS) to Version 16.4.0" (PDF). National Weather Service. 14 April 2025. Retrieved 2 August 2026.
  25. ↑ "Service Change Notice 25-89: Implementation of AIGFS, AIGEFS, and HGEFS" (PDF). National Weather Service. 9 December 2025. Retrieved 2 August 2026.
  26. ↑ "NOAA Deploys New Generation of AI-Driven Global Weather Models". National Oceanic and Atmospheric Administration. 17 December 2025. Retrieved 2 August 2026.
  27. ↑ "Farewell to the external AI models". ECMWF. 11 May 2026. Retrieved 2 August 2026.
  28. ↑ Options for Framing NOAA Weather and Water Modeling as a Foundational Component of the Broader US Weather and Water Enterprise (PDF) (Report). NOAA Science Advisory Board, Environmental Information Services Working Group. 10 March 2026. Retrieved 2 August 2026.
  29. ↑ "Public Information Statement 26-07: Proposed Replacement of GEFS Aerosol Products with GCAFS version 1.0" (PDF). National Weather Service. 28 January 2026. Retrieved 2 August 2026.
  30. ↑ "UFS-R2O". NOAA/NWS Virtual Lab. Retrieved 2 August 2026.
  31. ↑ "Advancements in Physics Parameterizations for Global Earth System Modeling at NOAA: Development of the GFSv17/GEFSv13/SFSv1 Physics Suite under the Unified Forecast System (UFS) Framework". Unified Forecast System, NOAA. November 2024. Retrieved 2 August 2026.
  32. ↑ "Public Information Statement 26-29: Soliciting Public Comments on the Proposed Upgrade to the Global Forecast System (Science Changes)" (PDF). National Weather Service. 15 April 2026. Retrieved 2 August 2026.
allikas: https://en.wikipedia.org/wiki/Global_Forecast_System

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