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metgrid ERROR: Error in ext_pkg_write_field using GEFSv12 reforecast data

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I am trying to use GEFSv12 reforecast data (available at to drive a regional simulation in WRF. I have pre-processed the grib files such that the required fields are contained in one file per forecast hour. Also, note that the fields vary in spatial resolution (0.25-deg at pressure levels below 700mb, else 0.50-deg), but I did not regrid them to a common resolution since grid can be defined per variable per level in the intermediate file.
I used Python package pygrib to read the grib data, and pywinter to write the corresponding intermediate files. I compared the results of the rd_intermediate.exe to results using intermediate files generated by ungrib. Upon running metgrid.exe, I encountered an error during the output module part:
2021-12-22 08:01:01.434 --- Initializing output module.
2021-12-22 08:01:02.893 --- ERROR: Error in ext_pkg_write_field
What might be causing this error? Should I regrid the 0.25-deg fields to 0.50-deg first for homogeneity?


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