The model output files are written or "packed" in an international WMO format known as GRIB. This packing format is described in detail in an NCEP document known as NCEP Office Note 388, available in PDF, WP5 or WP6 format at http://www.nco.ncep.noaa.gov/pmb/docs/on388/.
To handle the EDAS/ETA output fields in the GRIB format, one needs 1) the above documentation describing this format and 2) software to read and unpack this format. Several GRIB unpacking softwares are available at the following sites: