METplus Practical Session Guide (Version 5.0) | MET Tool: Plot-Data-Plane > Plot NetCDF Data

Plot NetCDF Data

The NetCDF file format is very flexible and enables the creation of self-describing data files. However, that flexibility makes it impossible to write general purpose software to interpret all NetCDF files. For that reason, MET supports a few types of NetCDF file formats, but does not support all NetCDF files, in general. It can ingest NetCDF files that follow the Climate-Forecast Convention, are created by the WRF-Interp utility, or are created by other MET tools. Additional details can be found in the MET Data I/O chapter of the MET User's Guide.

As described in The Field String, set name to the name of the desired NetCDF variable and level to define how to index into the dimensions of that variable. In the NetCDF level strings, use *,* to indicate the two gridded dimensions. For other, non-gridded dimensions, pick a 0-based integer to specify the value to be used for that dimension. For the time dimension, if present, selecting a 0-based integer does work, however you can also specify a time string in YYYYMMDD[_HH[MMSS]] format. The square braces indicate optional elements of the format. So 19770807, 19770807_12, and 19770807_120000 are all valid time strings. It is often easier to specify a time string directly rather than finding the integer index corresponding to that time string.

Run Plot-Data-Plane to plot quantitative precipitation estimate (QPE) data from a CF-compliant NetCDF file. First run ncdump -h to take a look at the header:

ncdump -h \

Note the following from the header:

    time = 1 ;
    y = 689 ;
    x = 1073 ;
   float P06M_NONE(time, y, x) ;
   // global attributes:
    :Conventions = "CF-1.0" ;

The variable P06M_NONE has 3 dimensions, but the time dimension only has length 1. Therefore, setting level = "(0,*,*)"; should do the trick. Also note that the global Conventions attribute identifies this file as being CF-compliant. Let's plot it, this time adding a title:

plot_data_plane \
${METPLUS_DATA}/model_applications/precipitation/QPE_Data/20170510/ \
${METPLUS_TUTORIAL_DIR}/output/met_output/plot_data_plane/ \
'name = "P06M_NONE"; level = "(0,*,*)";' -title "Precipitation Forecast" -v 4

Running at verbosity level 4, we see the range of values:

DEBUG 4: Data plane information:
DEBUG 4:       plane min: 0
DEBUG 4:       plane max: 101.086

If needed, run convert to reformat:

convert -rotate 90 \
${METPLUS_TUTORIAL_DIR}/output/met_output/plot_data_plane/ \

The next example extracts a specific time string from a precipitation analysis dataset:

ncdump -h \

Note the following from the header:

    time = 4 ;
    y = 428 ;
    x = 614 ;
    time1 = 1 ;
    float P06M_NONE(time, y, x) ;

Let's request a specific time string, specify a title, and use the same plotting range as above, rather than defaulting to the range of input data values.

plot_data_plane \
${METPLUS_DATA}/model_applications/precipitation/StageIV/ \
${METPLUS_TUTORIAL_DIR}/output/met_output/plot_data_plane/ \
'name = "P06M_NONE"; level = "(20170510_06,*,*)";' \
-plot_range 0 101.086 -title "Precipitation Analysis"

If running Plot-Data-Plane for multiple output times or data sources, consider using the -plot_range option to make their color scales comparable.

Lastly, let's plot output a NetCDF mask file that was created by an earlier version of MET's Gen-Vx-Mask tool.

ncdump -h ${METPLUS_DATA}/met_test/data/poly/NCEP_masks/

We will plot the NCEP_Region_ID variable with only 2 dimensions:

float NCEP_Region_ID(lat, lon) ;

Let's specify a different color table rather than using the default one.

plot_data_plane \
${METPLUS_DATA}/met_test/data/poly/NCEP_masks/ \
${METPLUS_TUTORIAL_DIR}/output/met_output/plot_data_plane/ \
'name = "NCEP_Region_ID"; level = "(*,*)";' \
-color_table $MET_BUILD_BASE/share/met/colortables/NCL_colortables/rainbow.ctable
When working with NetCDF files in MET, running ncdump -h is a great way to check their contents.