NAM model output on grid #218 (12km Lambert Conformal projection) is available in small subsets, called tiles. These files allow users to see high-resolution NAM output without downloading a series of very large files. These tiles are available for forecast hours every 3 hours out to 60 hours.
12-km NAM tiles are now available on the ftpprd.ncep.noaa.gov server in /pub/data/nccf/com/nam/prod/nam.YYYYMMDD/tiles.tHHz The directory for the current day contains the two most recent cycles (00z, 06z, 12z, 18z), and the tiles directories are listed at the very bottom of the list. Inside these subdirectories are files called:
ASCII files with the lat/lon of the grid points for each tile can be found on the ftp.emc.ncep.noaa.gov server in /mmb/mmbpll/g218tiles.latlon
For more information on grid 218 and other NAM grids, check out Office Note 388 Documentation from NCO.