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This import is available Delft-FEWS versions 2024.02 (basebuild 202402-50714143 or higher) and later.

The second time you run the import for the same T0, the import will be much faster (as long as you don't restart FEWS), because FEWS caches the .gpx files in the temp folder. This makes the import easier to test/debuglong as you don't restart FEWS), because FEWS caches the .gpx files in the temp folder. This makes the import easier to test/debug.

Known issues/warnings

1. The first time importing a certain forecast (with a specific T0), you may occasionally miss a timestep and get this warning: "WARN - Bad GRIB2 record in file cdms3://ecmwf-forecasts.s3.eu-central-1.amazonaws.com/ecmwf-forecasts?20250807/00z/ifs/0p25/oper/20250807000000-129h-oper-fc.grib2, skipping pos=85720605 cause=Please reduce your request rate. (Service: S3, Status Code: 503, Request ID: GT6E0AJF2J2GT1CZ, Extended Request ID: 0dj/YW262Zwm6s8wg8n4mKOwp1yzZqxNS38x9GnoGQ3o2hlBKu02xOzgHs/IdVT3wl3n5comEM1d/z2FF14+MFrmr7tntDg+9aY85Jns1KA=)". This is a problem and we're working on this (see FEWS-32610). 
2. Import runtimes can vary a lot (
3. The first time importing a certain forecast (with a specific T0), you'll see several warnings like "WARN - Table ecmf/name line      scaledValueOfSecondWavelength = missing() ;" → This is not a problem, you can ignore this warning.
4. When importing accumulated parameters, the first timestep (00h) will always give a warning like "WARN - Exception while parsing NetCDF data from url cdms3://ecmwf-forecasts.s3.eu-central-1.amazonaws.com/ecmwf-forecasts?20250807/00z/ifs/0p25/oper/20250807000000-0h-oper-fc.grib2. This url will be skipped. Message was: Allocation size must be greater than zero". → This is not a problem, you can ignore this warning.
5. The units defined in the .grib2 files don't always seem to be correct (e.g. radiation flux says W/m2 in the .grib2, but it actually seems to be a 3-hour accumulated J/m2 value). 
6. We have observed that certain parameters (e.g. Pressure_msl) take much longer than other parameters to import. This still needs to be investigated further.

Make the IdMap

Start by manually downloading an example .grib2 file from the ECMWF data browser and opening it in a NetCDF viewer (e.g. Panoply). Identify the parameters you would like to import. How to map the parameters depends on whether a parameter has a z-level (*_height_above_ground) and whether a parameter is accumulated or not (i.e. variables whose name changes in the grib2 file for each timestep).:

• Parameters without a z-level can be mapped directly, without defining locations. Use the main variable name listed in the grib2 file as external id.
• Parameters with a z-level should be mapped to an internalLocation that has a z-level defined (see next paragraph) combined with externalLocation="0". Use the main variable name listed in the grib2 file as external id.
• For parameters whose name changes at each timestep, such as accumulated variables (*_Accumulation), use the "Grib2_Parameter_Name" from the grib2 file as external id. 
• For isobaric parameters (*_isobaric), map the FEWS location to the layer index in the grib2 file. 

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Example IdMap for 2D parameters, 3D parameters using a z-level, and parameters whose names change at each timestep

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