From wgrib:formats.txt

                        Organization of the Grid

    Standard NMC practice is to store the grids in fortran order
starting from the north and working southward, and on the 0E and
working eastward.  No effort has been made in wgrib to implement
the scan order option in GRIB.  For lat-long grids, the dimensions
are 144 x 73.  The first point is 90N 0E, the second point is
90N 2.5E, and you can figure out the rest.  For Gaussian grids, the
dimensions are 192 x 94.  The first grid point is at 88.542N 0E,
the second grid point is at 88.542N 1.875E.  In theory, the Gaussian
latitudes (for a Gaussian grid) are determined by the zeros of
a long polynomial.  In practice, the Gaussian latitudes are almost
equally spaced.  For plotting purposes, I assume that the Gaussian
latitudes have a spacing of (88.542 - -88.542)/(94 - 1) degrees of
latitude.