Comparison of Forecast Skills between NCEP GFS Four Cycles and on the Value of 06Z and 18Z Cycles

NOAA NCEP runs its Global Forecast Systems (GFS) for medium-range weather prediction four times per day up to 16 days each, including 00Z, 06Z, 12Z and 18Z cycles. Most other international NWP centers perform data assimilation four cycles per day but run medium-range global weather prediction only two times per day, e.g., the 00Z and 12Z cycles. In this study we will first compare forecast skills between GFS four cycles in the past few years. Usage of conventional and satellite data observations between the four cycles will also be examined. Then we will investigate if the 06Z and 18Z cycles add any extra forecast skills compared to its respective earlier cycles, e.g., the 00Z and 12Z cycles, and at what forecast lead time the gain of extra skills is significant and the largest. Results of this study may shed light on the design of future NCEP operational forecast systems and the optimal use of available computational resources.