Grid-Stat Tool: Output

The output of Grid-Stat is one or more ASCII files containing statistics summarizing the verification performed and a NetCDF file containing difference fields. In this example, the output is written to the tutorial/out/grid_stat directory as we requested on the command line. That output directory should now contain 9 files, one each for the CTC, CTS, CNT, SL1L2, NBRCTC, NBRCTS, and NBRCNT ASCII files, a VSDB file, and a NetCDF difference fields file.

The format of the CTC, CTS, CNT, and SL1L2 ASCII files is the same as was described for the Point-Stat tool. The neighborhood method output is what's new for the Grid-Stat tool. Rather than comparing forecast/observation values at individual grid points, the neighborhood method compares areas of forecast values to areas of observation values. At each grid box, a fractional coverage value is computed for each field as the number of grid points within the neighborhood (centered on the current grid point) that exceed the specified raw threshold value. The forecast/observation fractional coverage values are then compared rather than the raw values themselves.

Since the lines of data in these ASCII file are so long, we strongly recommend configuring your text editor to NOT use dynamic word wrapping. The files will be much easier to read that way.

Open up the tutorial/out/grid_stat/grid_stat_120000L_20050807_120000V_nbrctc.txt NBRCTC file using the text editor of your choice and note the following:

• The format of this file is almost identical to that of the CTC file.
• The TYPE column indicates the line type. In this file, it is of the form NBRCTC, followed by the threshold value applied to the raw field, followed by the threshold value applied to the neighborhood fractional coverage field.
• The last column, INTERP_PNTS, now defines the size of the neighborhood over which the fractional coverage field was computed.
• The INTERP_MTHD column is omitted since it does not apply.

The exact same types of differences exist between the CTS and the NBRCTS files.

Close that file, open up the tutorial/out/grid_stat/grid_stat_120000L_20050807_120000V_nbrcnt.txt file, and note the following:

• The format of this file is NOT very similar to that of the CNT files.
• The format of the TYPE and INTERP_PNTS columns are similar to the NBRCTC and NBRCTS files.
• The two statistics included in this file are the Fractions Skill Score (FSS column) and the Fractions Brier Score (FBS column) and their corresponding confidence intervals. See section 5.3.3 of the MET User's Guide for a description of the neighborhood methods.

Close that file and execute the following command to view the NetCDF output of Grid-Stat:

ncview tutorial/out/grid_stat/grid_stat_120000L_20050807_120000V_pairs.nc &

Click through the variable names in the ncview window to see plots of the forecast, observation, and difference fields for each masking region. Now dump the header:

ncdump -h tutorial/out/grid_stat/grid_stat_120000L_20050807_120000V_pairs.nc

View the NetCDF header to see how the variable names are defined.