Dear all,

I would like to work with the GFS model data.
My source is : (it's maybe the only one!)
ftp://ftpprd.ncep.noaa.gov/pub/data/nccf/com/gfs/prod/

In subfolders, there are file named gfs.t00z.xxnn without extension.
I thought those files would be written with GRIB format, but it looks
it is not the case : I cannot open them with my GRIB tools.

What is the file format used for those files?
Is this mysterious format documented somewhere?

In advance, I thank you!
-Mathieu