The difference between 'gdas' and 'gfs' is actually in the analysis.  In operations, we create 2 analyses per cycle.  The first analysis is run shortly after the synoptic time (i believe it's 1.5 hours right now), and is used as the analysis for our operational, 15-day GFS forecast.  However, a later analysis is run at 3 hours past synoptic time (when more data has trickled in), where a shorter (GDAS), 9-hr forecast is run.  This 9-hr forecast is presumably of slightly better quality, as its analysis contains more observational information.  This 9-hr GDAS forecast is then used as the subsequent background for the next cycle's gfs AND gdas analyses. 

So for any given cycle (00, 06, 12, & 18) we have two analyses (gfs and gdas), as well as two sets of forecasts (gfs, out to 15 days, and gdas out to 9 hours) from their respective analyses. (April 2008 Daryl Kleist)

FAQ 1 GDAS脚本中gfs和fnl的区别是什么

'gdas'和'gfs'之间的区别实际上是在分析中。在业务中，我们每个周期创建2个分析。第一次分析是在天气时间后不久进行的（我相信它现在是1.5小时），并用作我们业务的15天GFS预报的分析。然而，后来的分析是在天气时间后3小时运行（当更多数据流入时），其中运行更短（GDAS），9小时预测。这个9小时的预测可能质量略高，因为其分析包含更多的观测信息。然后将这个9小时的GDAS预测用作下一周期gfs和gdas分析的后续背景场。

因此，对于任何给定的周期（00,06,12和18），我们有两个分析（gfs和gdas），以及两组预测（gfs，15天到9天，gdas到9小时）。分析。(April 2008 Daryl Kleist)