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In progress. All details still to be updated..

General requirements

Encoding format

WMO GRIB2 data format.

Missing values

Bitmaps shall be used to indicate missing values.

Grid and resolution

The fields have to be provided on...
Grids are defined in GRIB2 using an accuracy of 1/1000000 (one millionth) of a degree.

GRIB2 encoding

All data must be encoded following the required rules described below to achieve fully compliant LC-GCR format from all centres.

Encoding software

ECMWF makes available a GRIB decoding library (ecCodes) for the benefit of the WMO community. ecCodes can be freely downloaded from here and the documentation can be found here.

For more general information about GRIB2 format please refer to WMO Manual on Codes .

Encoding details

General encoding (TBA)

Specific details which should be encoded in GRIB2 sections 1 and 4:

Section 1
Octets	Key name	Value	Description	Comments
6-7	centre	X	WMO Centre's code (table below)
8-9	subCentre	0	WMO Sub-Centre's code if needed (table below)
10	tablesVersion	35	The latest WMO table^*1
20	productionStatusOfProcessedData	14	Lead Centre for Global Climate Reanalyses ^*2	To use during production phase
		15	Lead Centre for Global Climate Reanalyses test ^*2	To use during testing phase
21	typeOfProcessedData	0	Analysis products
		1	Forecast products

*1 New WMO tables version 35 (containing also new LC-GCR keys) will be officialy released by WMO later in 2025 (May-June)

*2 New codes for the LC-GCR (part of GRIB 2 tables version 35) approved by WMO in January 2025 (Manual on Codes (WMO-No. 306), Volume I.2, GRIB code table 1.3)

Section 4

Octets

Key name

Value

Description

8-9

productDefinitionTemplateNumber

0

Analysis and Forecast products (instantaneous)

(Analysis or forecast at a horizontal level or in a horizontal layer at a point in time (grib2/tables/17/4.0.table))

WMO Centre codes

The codes below are based on WMO Manual 306 - WMO Codes. Each organization must be uniquely identified by its WMO code. If necessary to distinguish between two organizations using the same WMO code the Sub-Centre one which differs must be provided.

Organisation	Acronym	WMO Centre code	Centre acronym^*1
China Meteorological Administration, China	CMA		babj
European Centre for Medium-Range Weather, UK	ECMWF	98	ecmf
Japan Meteorological Agency, Japan	JMA	34	rjtd
National Centres for Environmental Prediction, USA	NCEP	7	kwbc
National Aeronautics and Space Administration	NASA		nasa

Remarks:

*1 in ECMWF's ecCodes package

Examples of the required GRIB2 files

parameter	Sample file	GRIB metadata dump^*1
Time-mean 2 metre temperature	ecmf.an.grib2	ecCodes output
Time-mean mean sea level pressure	ecmf.an.grib2	ecCodes output
Time-mean total precipitation	ecmf.fc.grib2	ecCodes output

*1 using "grib_dump -O" command from ecCodes package

Remarks

sample files ecmf.*.grib2 files come from ECMWF's IFS model (data based on the current ERA5)
ecCodes Version 2.40.0 should be used to display correctly some LC-GCR related meta data
- currently it supports mainly centre=ecmf
  - support for other participating models (centre=babj/rjtd/kwbc/nasa) can be added only once we understand full details, how reanalyses are produced by the providers
    - exact encoding of time ranges will differ for different models depending on how daily sums are constructed etc
      - for example following applies to ERA5:
        Analysis are produced 1-hourly for 0-23h
        Average accumulations within a particular day=date are the average from the following forecasts:
        date-1 18UTC, step=7/to/12/by/1
        date 06UTC, step=1/to/12/by 1
        date 18UTC step=1/to/6/by/1