The Development of the NCEP Global Ensemble Forecast System Version 12

Xiaqiong Zhou aCPAESS, University Corporation for Atmospheric Research at NCEP/EMC and GFDL, Princeton, New Jersey

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Yuejian Zhu bNOAA/NWS/NCEP/EMC, College Park, Maryland

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Dingchen Hou bNOAA/NWS/NCEP/EMC, College Park, Maryland

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Bing Fu cIMSG at NOAA/NWS/NCEP/EMC, College Park, Maryland

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Wei Li cIMSG at NOAA/NWS/NCEP/EMC, College Park, Maryland

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Hong Guan dSRG at NOAA/NWS/NCEP/EMC, College Park, Maryland

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Eric Sinsky cIMSG at NOAA/NWS/NCEP/EMC, College Park, Maryland

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Walter Kolczynski cIMSG at NOAA/NWS/NCEP/EMC, College Park, Maryland

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Xianwu Xue dSRG at NOAA/NWS/NCEP/EMC, College Park, Maryland

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Yan Luo cIMSG at NOAA/NWS/NCEP/EMC, College Park, Maryland

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Jiayi Peng cIMSG at NOAA/NWS/NCEP/EMC, College Park, Maryland

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Bo Yang dSRG at NOAA/NWS/NCEP/EMC, College Park, Maryland

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Vijay Tallapragada bNOAA/NWS/NCEP/EMC, College Park, Maryland

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Philip Pegion eNOAA/Physical Sciences Laboratory, Boulder, Colorado

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Abstract

The Global Ensemble Forecast System (GEFS) is upgraded to version 12, in which the legacy Global Spectral Model (GSM) is replaced by a model with a new dynamical core—the Finite Volume Cubed-Sphere Dynamical Core (FV3). Extensive tests were performed to determine the optimal model and ensemble configuration. The new GEFS has cubed-sphere grids with a horizontal resolution of about 25 km and an increased ensemble size from 20 to 30. It extends the forecast length from 16 to 35 days to support subseasonal forecasts. The stochastic total tendency perturbation (STTP) scheme is replaced by two model uncertainty schemes: the stochastically perturbed physics tendencies (SPPT) scheme and stochastic kinetic energy backscatter (SKEB) scheme. Forecast verification is performed on a period of more than two years of retrospective runs. The results show that the upgraded GEFS outperforms the operational-at-the-time version by all measures included in the GEFS verification package. The new system has a better ensemble error–spread relationship, significantly improved skills in large-scale environment forecasts, precipitation probability forecasts over CONUS, tropical cyclone track and intensity forecasts, and significantly reduced 2-m temperature biases over North America. GEFSv12 was implemented on 23 September 2020.

© 2022 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Xiaqiong Zhou, xiaqiong.zhou@noaa.gov

Abstract

The Global Ensemble Forecast System (GEFS) is upgraded to version 12, in which the legacy Global Spectral Model (GSM) is replaced by a model with a new dynamical core—the Finite Volume Cubed-Sphere Dynamical Core (FV3). Extensive tests were performed to determine the optimal model and ensemble configuration. The new GEFS has cubed-sphere grids with a horizontal resolution of about 25 km and an increased ensemble size from 20 to 30. It extends the forecast length from 16 to 35 days to support subseasonal forecasts. The stochastic total tendency perturbation (STTP) scheme is replaced by two model uncertainty schemes: the stochastically perturbed physics tendencies (SPPT) scheme and stochastic kinetic energy backscatter (SKEB) scheme. Forecast verification is performed on a period of more than two years of retrospective runs. The results show that the upgraded GEFS outperforms the operational-at-the-time version by all measures included in the GEFS verification package. The new system has a better ensemble error–spread relationship, significantly improved skills in large-scale environment forecasts, precipitation probability forecasts over CONUS, tropical cyclone track and intensity forecasts, and significantly reduced 2-m temperature biases over North America. GEFSv12 was implemented on 23 September 2020.

© 2022 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Xiaqiong Zhou, xiaqiong.zhou@noaa.gov
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