wgrib2

wgrib2 usage and examples to use it with weather and climate grib2 files

1. wgrib2
Arulalan T
Scientist
India Meteorological Department

2. Introduction
•condainstall wgrib
•condainstallwgrib2
•Itsfreeandopensourcescientificsoftware to manage grib1 and grib2
(weather and climate data files)
•wgrib–v infile.grib1
•wgrib2–v infile.grib2(tryV,v2)

3. (1) How do I convert the entire file to binary?
$ wgrib2 grib_file-bin out.bin
(2) How do I get a verbose listing of the 20th message only?
$ wgrib2 -V -d 20 grib_file
If gribmessage 20 has submessages, then d 20 will get the first field of
the gribmessage. I.e, this will be the same as -d 20.1
(3) How do I extract the 20thand 30thgribmessage?
$ wgrib2 grib_file-match "(^20:^30:)" -bin binary_file
(4) How do I extract the first 10 records as a gribfile?
$ wgrib2 grib_file-for_n1:10 -gribnew_grib_file

4. (5) How do I extract records 34-66 from a file as a gribfile?
$ wgrib2 grib_file-for 34:66 -gribnew_grib_file
(6) How do I extract gribmessages 10,12,19 from a gribfile ?
$ wgrib2 old_grib-match '^(1|12|19):' -gribnew_grib
(7) How do I extract a range of dates from a file?
Example 1. Analysis file $ wgrib2 z500.gdas.199704.f06
1:0:d=1997040100:HGT:500 mb:6 hour fcst:
2:228571:d=1997040106:HGT:500 mb:6 hour fcst: ...
120:27173104:d=1997043018:HGT:500 mb:6 hour fcst:
The file contains the 500 mb geopotential height for the April 1997. To obtain
the data for a range of date:
$ wgrib2 z500.gdas.199704.f06 | awk '{d=substr($3,3); if (d >=1997042400 &&
d <=1997042512) print $0}' FS=':' | wgrib2 z500.gdas.199704.f06 -i-grib
z500subset.grb

5. Example 2. Extract a range of forecast times
$ wgrib2 t250.03.2015080900.daily.grb2
1:0:d=2015080900:TMP:250 mb:6 hour fcst:
2:20236:d=2015080900:TMP:250 mb:12 hour fcst: .. 456:8689473:d=2015080900:TMP:250 mb:2736 hour fcst:
To extract a range of forecasts, you can put the verification time into the inventory
$ wgrib2 t250.03.2015080900.daily.grb2 -vt-s 1:0:vt=2015080906:d=2015080900:TMP:250 mb:6 hour fcst: 2:20236:vt=2015080912:d=2015080900:TMP:250 mb:12 hour fcst: ...
Modifying example 1
$ wgrib2 t250.03.2015080900.daily.grb2 -vt-s | awk '{d=substr($3,4); if (d >=2015081000 && d <= 2014081012) print $0}' FS=':' | wgrib2 t250.03.2015080900.daily.grb2 -i-gribsubset.grb4:60273:d=2015080900:TMP:250 mb:24 hour fcst: 5:80131:d=2015080900:TMP:250 mb:30 hour fcst: 6:99799:d=2015080900:TMP:250 mb:36 hour fcst:

6. (8) CMC files have some variables which don't have a name. wgrib2 doesn't
include the local extensions from CMC. AFAIK, the CMC gribtables follows the
NCEP gribtable except where they don't. (How does that helps me?) So you
may be able to get most of the fields right by using ntthe NCEP tables. This can
be done changing the centerflag to NCEP (7).
$wgrib2 -set center7 infile.grib2(In memory)
$wgrib2 -set center7 infile.grib2 -grib_outoutfile.grib2 (In outfile)
(9) Use append option to append on existing grib2 files
$wgrib2 -set center7 infile.grib2 -append -grib_outoutfile.grib2

7. (10) I am generating a text dump (CSV) and the size of the file is really large. If you set the grid point values to "undefined", they won't print out.
$wgrib2 grib_file-undefine out-box 30:40 -10:10 -csv out.txt
The grid points outside of the box are set to undefined. The -csv options tries to print the entire grid but finds only the values between 30N-40N and 10W-10E are defined.
(11) I am generating a text dump (CSV) and the size of the file is really large, I am only interested in variable XYZ when it has values larger than 10
$wgrib2 grib_file-match ':XYZ:' -undefine_val-9e20:10" -csv output.txt
(12) How do I extract small region from big domain in grib2 file
$wgrib2-small_gribLonW:LonELatS:LatNfile_name
$wgrib2 fcst.grb2 -small_grib10:20 -20:20 small_out.grb

8. (13) I tried using the small_griboption but the files are bigger than the original.
By default, The small_griboption writes a regional subset in simple packing.
This requires less CPU resources but produces larger files than jpeg or complex
packing.
To use the same packing as the original file, use the "-set_grib_typesame"
option. OR –set_grib_typejpegOR –set_grib_typecomplexOR –set_grib_type
complex2Or –set_grib_typecomplex3
(14) How do I extract a few variables and write out into new grib2 file ?
$wgrib2 infile.grib2 -match "(VIS:surface:60 min fcst:|HGT:cloudceiling:60 min
fcst:)" –gribout.grib2
$wgrib2 infile.grib2 -match "(VIS:surface:60 min fcst:|HGT:cloudceiling:60 min
fcst:)" –grib_outout.grib2
$wgrib2 infile.grib2 -match "(VIS:surface:60 min fcst:|HGT:cloudceiling:60 min
fcst:)" –append –grib_outout.grib2

9. (15)I want to modify some existing gribfiles. For example, I want to make sure
the humidity (RH, SPFH) is positive.
$wgrib2 test.grb-rpn"0:max" -set_grib_typec2 -grib_outnew.grb
-rpn0:max, replaces the grid point values with max(0,grid_point_value)
(16) My software won't handle the level "30-0 mb above ground". How do I
change the level to "15 mb above ground"?
IF structure
$wgrib2 in.grb-if ":30-0 mb above ground" -set_lev"15 mb above ground" -
endif -gribout.grb
(17) How do I combine multiple grib2 files
$catinfile1.g2 infile2.g2 infile3.g2 infile3.g2 > outfile.grib2

10. (18) Masking data: I want set all oceanic values to undefined. Suppose LAND is a
gribfile with the land mask (land=1, water=0) with the same grid as the data file
(data.old) Make a new file with the land mask as the first record.
$cat LAND data.old> data.tmp
$wgrib2 data.tmp\
-if '^1:’ -rpn'1:==:sto_1’ -fi \
-not_if'^1:' -rpn'rcl_1:mask' -set_grib_typesame \-set_scalingsame\
-grib_outdata.new
(19)My gribfile uses the special value of -999.9 as the undefine value. (Grid
points with a value of -999.9 are considered to be undefined). Using special
values as undefined values is outside of the gribstandard and should be
avoided. To convert a file that uses -999.9 to the gribstandard, you should do
$wgrib2 IN.grb-undefine_val999.9 -set_grib_typesame -grib_outOUT.grb

11. (20) The -merge_fcstoption will try to combine adjacent messages by
increasing the time period for forecast average, accumulation, minimum
and maximum. For example,
$ wgrib2 prate.201404.ts -for 1:4
1:0:d=2014040100:PRATE:surface:0-1 hour avefcst:
2:13083:d=2014040100:PRATE:surface:1-2 hour avefcst:
3:26587:d=2014040100:PRATE:surface:2-3 hour avefcst:
4:40437:d=2014040100:PRATE:surface:3-4 hour avefcst:
$ wgrib2 preas.201404.ts -for 1:4 -merge_fcst4 all.grb(listing of input)
$ wgrib2 all.grb
1:0:d=2014040100:PRATE:surface:0-4 hour avefcst:
Similar way, automatically compute accumulation, minimum,maximumbased
on input meta information available in the input.grib2 file.

12. (20) The -merge_fcst-make daily accumulated rainfall from four 6-hourly accumulated rain
$ cat fhr06 fhr12 fhr18 fhr24 > IN.grb
$ wgrib2 IN.grb| sort -t: -k4,4 -k5,5 -k6,6n | wgrib2 -iIN.grb-gribOUT1.grb
$ wgrib2 OUT1.grb -merge_fcst4 OUT2.grb
$ wgrib2 OUT1.grb -if ":APCP:” -merge_fcst4 OUT2.grb
(21) how to change the date code in a grib2 file ex. change the analysis/initial time date to 12Z of 5thJan 2023
$wgrib2 -match "^[0-9]*(:|\.1)" IN.grb-set_date2023010512 -GRIB OUT.grb
(22) How do I extract a particular lat, lonvalues? get values at (30N, -90W) and (40N, -80N)
$wgrib2 IN.grb-lon-90 30 > location1.txt
$wgrib2 IN.grb-lon-80 40 > location2.txt
$wgrib2 IN.grb-lon-90 30 -80 40 > locations.txt

13. (23) The GFS model has output every 3 hours in the files: gfs.t00z.pgrb2.1p00.fHHH HHH=000, 003, 006, 009, etc
The APCP (accumulated precip) fields of the following format
gfs.t00z.pgrb2.1p00.f003: has APCP:surface:0-3 hour accfcst:
gfs.t00z.pgrb2.1p00.f006: has APCP:surface:0-6 hour accfcst:
gfs.t00z.pgrb2.1p00.f009: has APCP:surface:6-9 hour accfcst:
gfs.t00z.pgrb2.1p00.f012: has APCP:surface:6-12 hour accfcst:
gfs.t00z.pgrb2.1p00.f015: has APCP:surface:12-15 hour accfcst: ..
I want a file with the 3 hourly accumulations like
1:0:d=2017041800:APCP:surface:0-3 hour accfcst:
2:97943:d=2017041800:APCP:surface:3-6 hour accfcst:
3:195886:d=2017041800:APCP:surface:6-9 hour accfcst:
4:301974:d=2017041800:APCP:surface:9-12 hour accfcst:
5:383627:d=2017041800:APCP:surface:12-15 hour accfcst: ..
You can use the -ncep_normto make the 3 hourly accumulations of the APCP by
$ cat gfs.t00z.pgrb2.1p00.f0?? | wgrib2 --match ':APCP:' -if ':APCP:' -ncep_normapcp.grb2
Results are $ wgrib2 apcp.grb2
1:0:d=2017041800:APCP:surface:0-3 hour accfcst:
2:97943:d=2017041800:APCP:surface:3-6 hour accfcst:
3:195886:d=2017041800:APCP:surface:6-9 hour accfcst:
4:301974:d=2017041800:APCP:surface:9-12 hour accfcst:

14. (24)In the operational CFSv2 time series, V does not follow U and the forecasts are not in order. When using -
new_grid, the vector fields must be adjacent (u-component then v-component).
$wgrib2 IN.grb| sed-e 's/:UGRD:/:UGRDa:/' -e 's/:VGRD:/:UGRDb:/' | sort -t: -k3,3 -k6n,6 -k5,5 -k4,4 | wgrib2 -
iIN.grb-gribOUT.grb
(25) Compute wind speed and direction and append into same input file. We need to make sure both u-wind
and v-wind are aligned properly
$wgrib2 -match "(UGRD|VGRD)" infile.grb2 -wind_speedtmpfile-wind_dirtmpfile
$cat tmpfile>> infile.grb2
(26) HowdoIinterpolate/extrapolatetodifferentgridresolutionofwinds?
$wgrib2 IN.grb| sed-e 's/:d=\([0-9]*\):\([A-Z]\)\([^:]*\)/:d=\1:\3_\2:/' | sort -t: -k3,3 -k5,5 -k6,6 -k4,4 | wgrib2
-iIN.grb-new_grid_windsearth -new_gridlatlon0:144:2.5 -90:73:2.5 OUT.grb
(27) I have grib2 files in WE:NS order, how do I put them into WE:SN order?
Use -new_gridto a new grid. Just make the new grid the same as the old grid except for a WE:SN order.

15. (28) I wanted to find the min TMP2M for a given year from CFSR. IN.grb= time series of TMP2m (only) for the
given year # create an inventory where record 1 is last
$wgrib2 IN.grb-for 2:: > junk.inv
$wgrib2 IN.grb-d 1 >> junk.inv# process the file with record 1 last
$wgrib2 -i<junk.invIN.grb-if "^2:" -rpn"sto_1" -fi -rpn"rcl_1:min:sto_1" -if "^1:" -set_ave"0-1 year min anl" -
grib_outOUT.grb
(29) How do I convert grib2 to netcdfformat ?
$ wgrib2 infile.grib2 -netcdfoutfile.nc
$ wgrib2 infile.grib2 -nc_nlev4 -netcdfoutfile.nc# to bring proper 4 dimensional axis
(30) The -lolaoption with nlat=nlon=1 and dlat=dlon=1 (or any non-zero value)
binary:$ wgrib2 IN.grb-no_header-lola"10:1:1" "20:1:1" grid.binbin
text: $ wgrib2 IN.grb-lola"10:1:1" "20:1:1" grid.txttext
CSV: $ wgrib2 IN.grb-lola"10:1:1" "20:1:1" grid.grbgrib(converting to grib)
$ wgrib2 grid.grb-csv grid.csv(converting gribto CSV)

16. (31) I have a file with var246 that I want to change to the standard UGRD at 100 m above
ground.
$wgrib2 IN.grb-if ":var246:" -set_varUGRD -set_lev"100 m above ground" -fi -gribOUT.grb
(32) I have 80 ensemble members that have WIND (wind speed) at 10m. I want to find the
probability the the WIND is greater or equal to 15 m/s based on the percentile of ens
members >= 15 m/s.
ensemble data is at $input/flx.memNNN.YYMMDDHHwhere NNN=001..080 WIND is only
defined at 10 meters above ground
$ cat flx.mem??? | wgrib2 --match ":WIND:" -rpn"15:>=" -ens_processingensstat.grbx
$wgrib2 ensstat.grb-match ":ensmean" -set_grib_typec3 -set_prob1 1 1 15 15 -grib
wind_ge_15.grb

17. g2ctl.pl
For analyses:$ g2ctl -O grib2_file > grib2_file.ctl$ gribmap-O -igrib2_file.ctl$ gradsga-> open grib2_file.ctl
For forecasts (end of averaging period):$ g2ctl grib2_file > grib2_file.ctl$ gribmap-igrib2_file.ctl$ gradsga-> open grib2_file.ctl
For forecasts (start of averaging period):$ g2ctl -b grib2_file > grib2_file.ctl$ gribmap-b -igrib2_file.ctl$ gradsga-> open grib2_file.ctl
-verf.. use end of ave/accperiod or
fcsttime (default)
run gribmapwith no option
-0 .. use analysis times
run gribmapwith gribmap-0
-b .. use start of
averaging/accumulation period
run gribmapwith gribmap-b
-365 .. use 365 day calendar
-no_profile.. no z coordinate
-raw .. use a raw grid
-ens"e1,..,en" .. a list of quoted
ensemble names

18. References
https://www.cpc.ncep.noaa.gov/products/wesley/wgrib2/
https://www.ftp.cpc.ncep.noaa.gov/wd51we/wgrib2/tricks.w
grib2
https://www.ftp.cpc.ncep.noaa.gov/wd51we/wgrib2/tricks.ch
eap
https://www.cpc.ncep.noaa.gov/products/wesley/g2ctl.html