# What is the difference between GFS analysis and GFS forecast data?

gfsanl_3_20151201_0000_006 means that the analysis was made at 0000 UTC and is valid at 0600 UTC, doesn't it? But for how long, 3 hours? And what is the difference to gfs_4_20151201_0000_006, which is listed under GFS forecast? I cannot figure out the difference between those two.

I'm no expert at this, I've just been working with a variety of gfs gribs for a while now. The only thing I know about them is what I've read and I'll cite them here. I don't know where you got those files. It looks like you're looking at the files that are sub areas, but in general the file format goes as shown more clearly on this website:

data/nccf/com/gfs/prod/gfs.YYYYMMDDHH/gfs.tHHz.formidffhour !GRIB_version/ncep/model/#000/YYYYMMDDHHNNFfff/parm/level! ######


Grid #004, 0.5x0.5 degree lat/lon grid, formid = pgrb2 (Hours F000-F180) GRIB_version=grib2 (grid number appears as #000) Note: fhour: anl, f00, f06, f12....f384 (note: 2 or 3 digit fhour as on ftp server) GRIB2 Note: "model date" and "forecast hour" fields are not separated by "/"