What is GRIB?
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. Nevertheless, because of its widespread acceptance, the WMO has stated that Edition 1 will remain an official WMO standard for the foreseeable future. The CMC currently uses Edition 1.
- GRIB Edition 2 : recently became an official WMO 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.
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.
Please Note: GRIB files require appropriate decoding software, without which the data cannot be viewed or processed in any useful way.
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