Forecasting with the GFS is great for wind, height, precipitation, moisture movement and atmosphere dynamics. The disadvantages of the GFS are temperature and severe indices. ETA is really good when it comes to forecast severe weather and temperatures, but poor on atmosphere forecasting. I used the GFS to forecast CAPE and values were only around 250 J/Kg and ETA showed 2500 J/Kg. The ETA was accurate because late afternoon thunderstorms exploded with violent downburst in scattered locations.  However, the GFS showed rainfall would be around near .75 inches and the final total was .81 inches after the thunderstorms dump their rain.