If you are running WRF 3.x series with the NCEP GFS data updated some time in 2019 you may have found an error along the lines of:

ERROR: The mandatory field TT was not found in any input data.

There may also be an error with metgrid.exe where you get:

ERROR: Error in ext_pkg_write_field

How to fix?

This is because the GFS data was updated in June 2019 with a new format (solution credit of this link, retrieved 12/9/2019).

The solution is rather simple: compile the version 4.0 of the WRF PreProcessing System (WPS) and use ungrib.exe from there. You don’t need to change the Vtable or anything else in your existing 3.x WRF+WPS installation.

This is a quick tip post. They are written in a way to help users quickly resolve a problem that I ran into in my daily work and usually don’t go in depth about the details of ‘why’. Please feel free to comment or contribute to the knowledge.