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.

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