VAPOR stands for Visualization and Analysis Platform for Ocean, Atmosphere, and Solar Researchers. It is a software system providing an interactive 3D visualization environment that runs on most UNIX ,Windows and Mac systems equipped with modern 3D graphics cards. The home of the software is https://www.vapor.ucar.edu :
VAPOR has it own internal data model and NWP data has to be converted into the VAPOR format. There are a set of command line tools that can convert NetCDF input data into the VAPOR format but there is no such tool available for GRIB.
Metview's VAPOR Prepare icon helps to overcome this difficulty and allows converting ECMWF GRIB data into the VAPOR format. Detailed instructions on how to use this icon can be found here.
Once the data has been converted just right-click Visualise the VAPOR Prepare icon to start up VAPOR with the newly created dataset