Although all meteorological models use the same observations, there are
three significant differences between EDAS and FNL: horizontal, vertical,
and temporal resolution. EDAS has better resolution in all categories.
For the case you sent me I re-ran the EDAS trajectory using starting
heights of 300, 400, and 500 m agl. There are large differences in the
first 24 hours. The 400 m trajectory corresponds more with your 500 m
FNL. EDAS vertical resolution is every 25 hPa, FNL resolution is limited
to mandatory surfaces: 1000, 925, 850 hPA etc. The usual procedure should
be to run trajectories at several heights and locations about the point of
interest -- if the trajectories are similar then the confidence level is
high -- if they diverge then there is more uncertainty.
Roland Draxler
NOAA ARL