The most current month of model output is available online through the ds335.0 data page. Online archives are populated daily with model output generated two days prior to the current date. Older historical files, beginning in December 2002, are available upon request. Higher resolution versions of RUC, NAM, and higher resolution global GFS and GFS Ensemble are available starting November 1, 2006. All model output files are stored in their native GRIB1 and GRIB2 formats.

Information on the GRIB data format can be found here.

NCEP Grid definitions can be found here.

A similar NCDC dataset can be found here.

A similar NCEP dataset can be found here.

Unidata's THREDDS catalog provides descriptions and model data access here.

Historical Unidata Internet Data Distribution Global Observational Data can be found in ds336.0.