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 a  regular latitude‐longitude grid at the resolution that is best matching the native resolution of the direct  model output.
  • Grids are defined in GRIB2 using an accuracy of 1/1000000 (one millionth) of a degree.
  • If several limited areas will be provided  they should be merged into one larger area on a regular lat-lon grid, with a missing value indicator in the grid-points not covered.

GRIB2 encoding

All data must be encoded following the required rules described below to achieve fully compliant LC-WFV 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. EcCodes provides a simplified access to GRIB2 headers through a set of virtual keys documented here.

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

Encoding details


General encoding

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

Section 1
Octets Key nameValueDescription
6-7centreXWMO Centre's code (table below)
8-9subCentreXWMO Sub-Centre's code if needed (table below)
10tablesVersion19The latest WMO table

Production data

  1Test data
21typeOfProcessedData0Analysis products
  1Forecast products
Section 4
OctetsKey name





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.

OrganisationAcronymWMO Centre codeWMO subCentre codeCentre acronym*1

European Centre for  Medium-Range Weather, UK

ECMWF98 N/Aecmf
Met office, UKUKMO74 N/Aegrr
Fleet Numerical Meteorology and Oceanography Center, USAFNMOC58 N/Afnmo
Environment and Climate Change Canada, CanadaECCC54 N/Acwao
National Centres for Environmental Prediction, USANCEP7 N/Akwbc
Météo France, FranceMETFR84 N/Alfpw
Deutscher Wetterdienst, GermanyDWD78 N/Aedzw
Bureau of Meteorology, AustraliaBoM1 N/Aammc
Laboratoire D'Océanographie Physique et Spatiale, FranceLOPS84202lops
Japan Meteorological Agency, JapanJMA34 N/Arjtd
Korea Meteorological Administration, Republic of KoreaKMA40 N/Arksl
Puertos del Estado, SpainPRTOS214 N/Alemm
Danmarks Meteorologiske Institut, DenmarkDMI94 N/Aekmi

National Institute of Water and Atmospheric Research, New Zealand

NIWA204 N/Aniwa

Det Norske Meteorologiske Institutt, Norway

METNO88 N/Aenmi

Servicio de Hidrografía Naval, Servicio Meteorológico, Argentina

SHNSM41 N/Asabm

New Zealand MetService

NZMS69 N/Anzkl
Servizio Meteorologico dell'Aeronautica Militare, ItalyMETEOAM80 N/Acnmc


*1 in ECMWF's eCcodes

Example of the validity type encoding


This example describes an instantaneous field  valid on 20120103 00Z from a forecast starting on 20120101 00Z (time step=48 hours) .

  • In bold, the values are fixed. They are meant to be used by all partners
  • In green, these are the values for the example.
Time ( instantaneous )
Start of forecast ( section 1 )




Meaning of valuesGrib_api values
12Significance of Reference Time1Start of forecast 
13-14Year (four digits)2012year of start of forecast




15Month01month of start of forecast
16Day01day of start of forecast
17Hour00hour of start of forecast
 section 4 e.g. template 4.1
18Indicator of unit of time range 1Hour 
19-22Forecast time48Forecast stepstepType=instant, step=48

Examples of  the required GRIB2 files


Sample file

10 metre U wind component 


10 metre V wind component 

Mean wave period based on second momentwave.mp2.grib2
Mean wave directionwave.mwd.grib2
Peak wave periodwave.pp1d.grib2

Significant height of combined wind waves and swell