There are several ways you can do this:
1. Use SKINTEMP from a regular GFS forecast. This means you will need to run a separate ungrib.exe job just for SKINTEMP from that dataset.
2. Create a Vtable that will ungrib the surface temp, and save it under a different name (e.g., Vtable.SKINTEMP), then change the prefix in the ungrib section of the namelist, and add it to the prefix under the ungrib section. So you will run ungrib once, per normal. Then run again, and in your namelist.wps file, you should have something like:
&ungrib
out_format = 'WPS',
prefix = 'SKINTEMP'
Then you will run metgrid, and your namelist should look like:
&metgrid
fg_name = 'FILE', 'SKINTEMP',
io_form_metgrid = 2,
3. If you are using Version 3.1.1 or later, SKINTEMP is no longer mandatory. You may run the utility program avg_tsfc.exe for multiple times, and create an averaged surface temp field TAVGSFC. Add this field to the &metgrid section of the namelist:
&metgrid
fg_name = 'FILE'
constants_name = './TAVGSFC'
In addition to the above, you will need to edit WPS/metgrid/METGRID.TBL. Find the section for SKINTEMP and remove mandatory = yes. This should allow you to finish metgrid.exe, and later when you run real.exe, it will use this field instead of SKINTEMP.
1. Use SKINTEMP from a regular GFS forecast. This means you will need to run a separate ungrib.exe job just for SKINTEMP from that dataset.
2. Create a Vtable that will ungrib the surface temp, and save it under a different name (e.g., Vtable.SKINTEMP), then change the prefix in the ungrib section of the namelist, and add it to the prefix under the ungrib section. So you will run ungrib once, per normal. Then run again, and in your namelist.wps file, you should have something like:
&ungrib
out_format = 'WPS',
prefix = 'SKINTEMP'
Then you will run metgrid, and your namelist should look like:
&metgrid
fg_name = 'FILE', 'SKINTEMP',
io_form_metgrid = 2,
3. If you are using Version 3.1.1 or later, SKINTEMP is no longer mandatory. You may run the utility program avg_tsfc.exe for multiple times, and create an averaged surface temp field TAVGSFC. Add this field to the &metgrid section of the namelist:
&metgrid
fg_name = 'FILE'
constants_name = './TAVGSFC'
In addition to the above, you will need to edit WPS/metgrid/METGRID.TBL. Find the section for SKINTEMP and remove mandatory = yes. This should allow you to finish metgrid.exe, and later when you run real.exe, it will use this field instead of SKINTEMP.