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Numerical Forecast Systems

Info on the Ensemble forecasts using the Global Spectral Model

Global EPS Report to WMO on NCEP Global Ensemble Forecast System (GEFS) pdf

At NCEP the current NCEP Global Ensemble configuration consists of runs at 00Z, 06Z, 12Z 18Z each day (available through anonymous ftp from public servers)

Three different types of forecast files are generated from each run:
A T574L64 high resolution control (file name for, e.g., a 24 hr fcst at 00Z is gfs.t00z.pgrbf24) out to 8 days, after which this run gets truncated and is run out to 16 days at a T126L64 resolution
A lower resolution ensemble control (T254L42) that is started with a truncated T574L64 highbrid analysis and run out to 8 days, then reduced horizontal resolution (T190) and run out to 16 days, labeled as (gec00.t00z.pgrb(a/b)f24)
20 perturbed forecasts each run out to 16 days at T254L42 (0-8 days) and T190L42 (8-16 days) horizontal and vertical resolution. The tropical storm relocation technique has been used to re-install observed tropical storm location to model initial state. The initial perturbations are generated using Ensemble Transform with Rescaling (ETR) method**. The stochastic total tendency perturbation (STTP) is introduced to enhance model uncertainty. Each perturbed forecast will be labled as gep(01/02/03...).t00z.pgrb(a/b)f24

The examples of files given above are pressure grib files that also contain flux and surface related fields. For information and software on how to read grib format files, using different platforms, click here . If you have questions regarding the ensemble forecasts you can contact Yuejian Zhu at
**(See Wei et al., 2007; Initial perturbations based on the ensemble transform (ET) technique in the NCEP global operational forecast system; Tellus)