Review of NCEP GFS forecast skills and major upgrades

Forecast skills of global numerical weather prediction (NWP) models have been steadily improving as a result of improved model dynamics and physics, more observations and faster computers. This presentation reviews the forecast skills and their changes of a few international NWP models in the past twenty years, with a focus on the NCEP global forecast systems (GFS). The evaluation includes geopotential height anomaly correlation, tropical wind bias, and precipitation skill scores. Instances of significant improvements in GFS forecast skills are linked, in retrospect, to major model upgrades related to model resolution, dynamics and physics packages, and data assimilation schemes. Recent and planed future GFS upgrades and remaining challenges are discussed.