NCEP forecast files often have the U and corresponding V fields in the same grib message.
(U and V are submessages.) Typically wgrib2 converts submessages into individual messages.
There is already some facility to make submessages by the -tosubmsg
option but that option can't combine the U and V fields alone. The -ncep_uv
option allows you to duplicate the practice of combining the U and V fields.
$ wgrib2 test.grb2 -ncep_uv output.grb
1:0:d=2005090200:HGT:1000 mb:60 hour fcst:lon=270,lat=20,val=121.3
2:133907:d=2005090200:HGT:975 mb:60 hour fcst:lon=270,lat=20,val=344.4
See also: -tosubmsg