Modifination to wgrib2, distributed under terms of the GNU General Public License.
An optional parametetr is added to handle JMA's nowcast 250 data. You can use it as follows.
-csv_nz FILE_PATH min_value
ex: -csv_nz sample_output.csv 0.25
"min_value" is a lower threshold value to filter the data records. Records for the error information are all omitted. A record of the output file follows the format described below.
Reference time, end time, forecast time offset, longtitude, latitude, data value