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Ensemble forecasts attempt to address the uncertain nature of NWP.
Both initial condition errors and errors in the formulation of the physics forcing are compounded in NWP non-linear models, degrading the accuracy of forecasts. To account for increased uncertainty from growing instabilities, the atmospheric component of NCEP operational global ensemble modeling suite, Global Ensemble Forecast System (GEFS), utilizes perturbations in EnkF 6-hour forecasts from the hybrid data assimilation to generate initial perturbations and Stochastic Perturbation of Physics Tendency (SPPT) and Stochastic Kinetic Energy Backscatter (SKEB) schemes to account for model errors.
The current system, effective 2020SEP, produces 120 perturbation forecasts per day, 30 per cycle, at C384L64 resolution for 16 days, and those for 00Z cycles are extended to 35days at the same resolution. The model output presented in this data base is at half degree latitude by half degree longitude grid, with 85 most commonly used variables.