DWD ICON-EU GRIB2 data incompatible after switch to CCSDS packing

[Zerosimi]

WPS version: 4.5
Affected component: ungrib.exe
Affected data source: DWD ICON-EU Open Data (opendata.dwd.de)

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Description

From 16 June 2026, DWD changed the GRIB2 data representation of their ICON, ICON-EU and ICON-D2 Open Data products from simple packing (grid_simple) to CCSDS lossless compression (grid_ccsds).

Reference: DWD Open Data News, Mai 2026 (scroll down for english version)

metgrid fails because of missing mandatory variables, after running ungrib with the new ICON-EU grib2 files. In the metgrid logfiles list many variables as not found. This is most likely due to an incorrect ungrib run, even though ungrib completes successfully.

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Ungrib logfile

The ungrib log file is filled with these messages:

  ERROR extracting field gf_getfld =           12
 getdrstemplate: DRS Template           42  not defined.

Metgrid error

Processing domain 1 of 2
Processing 2026-06-17_12
   /path/to/wps/FILE
ERROR: The mandatory field TT was not found in any input data.
The mandatory field TT was not found in any input data.

Steps to reproduce

1. Download current ICON-EU GRIB2 data from https://opendata.dwd.de/weather/nwp/icon-eu/grib/
2. Merge them following the logic of the ICON-EU thread in the WRF forum
3. Link files with link_grib.csh and run ungrib.exe with Vtable.ICONm
4. Observe that mandatory field TT is reported as not found

Verify packing type:

grib_ls -p packingType <input_file> | head -5

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Workaround

Repack the GRIB2 files from CCSDS to simple packing using ecCodes before running link_grib.csh and ungrib.exe. Requires ecCodes

grib_set -r -w packingType=grid_ccsds -s packingType=grid_simple <input_file> <output_file>

The -w packingType=grid_ccsds flag restricts conversion to CCSDS messages only, leaving any already-simple messages unchanged. After conversion, the standard ungrib workflow proceeds without modification.