What is GRIB?

The different GRIB versions

GRIB is a file format for the storage and transport of gridded meteorological data, such as Numerical Weather Prediction model output. It is designed to be self-describing, compact and portable across computer architectures. The GRIB standard was designed and is maintained by the World Meteorological Organization.

Over the years, the WMO issued three editions of the GRIB standard:

  • GRIB Edition 0 : now obsolete, unsupported, and rarely used.
  • GRIB Edition 1 : no longer the most current WMO GRIB edition, the format of Edition 1 has been frozen from future enhancements. However, due to it's usage in the World Area Forecast system of the ICAO, it it still recognized by the WMO. In the medium term, the CMC will no longer produce data in this format.
  • GRIB Edition 2 (Requires Acrobat Reader to view) (GRIB2): the GRIB2 format represents an enlarging and a significant modernization of the GRIB standard. It is being phased in by the ECMWF and some national Numerical Weather Prediction institutions, notably in the US and Europe. A significant modernization and broadening of the GRIB standard, Edition 2 is not backward-compatible with Edition 1.

Before 2010, the CMC was offering it's data only in GRIB1 format. Starting in 2010, the CMC is offering data in GRIB1 and GRIB2 format in order for it's client to be able to migrate toward the new GRIB2 format. In 2011, the CMC aims to distribute only in GRIB2 format.

Who uses it, and what for?

GRIB data is used by individuals, institutions and businesses who have the means and motivation to tap into numerical data from weather models in the rawest possible form. GRIB data is often only one step removed from the original model output. Once decoded, the data can be post-processed for visualization, or used as input for numerical weather prediction applications that require gridded data.

What is in a GRIB file?

A GRIB file contains one or more data records, arranged as a sequential bit stream. Each record begins with a header, followed by packed binary data. The header is composed of unsigned 8-bit numbers (octets). It contains information about :

  • the qualitative nature of the data (field, level, date of production, forecast valid time, etc),
  • the header itself (meta-information on header length, header byte usage, presence of optional sub-headers),
  • the method and parameters to be used to decode the packed data,
  • the layout and geographical characteristics of the grid the data is to be plotted on.

Software to use GRIB format

The Meteorological Service of Canada does not distribute publicly any decoding or visualization software for the GRIB format. Here is a non exhaustive list of links to find software to manipulate and display GRIB data::

GRIB references

GRIB1

  • WMO GRIB Edition 1
  • NCEP Office Note 388 containing the same information than the WMO document, and describes the deployment of the NCEP GRIB standard, Edition 1. The parameters used in the type of levels used in GRIB from the CMC are compatible with tables published in the NCEP Note 388.

GRIB2