A GRIB grid is a binary file format developed for use in the weather and meteorological industries to transport and manipulate weather data and is the foundation of weather forecasts.
The file format is maintained by the World Meteorological Organization. The format is described in detail at http://www.wmo.int/pages/prog/www/WDM/Guides/Guide-binary-2.html.
File name extensions
World Meteorological Organization .GRB files are similar to grid files and can be loaded to create a grid based map (e.g. Home | New Map | Contour), or when using the functions in the Grid tab.