GRIB Weather PlugIn

OpenCPN has a lightweight grib weather file viewer plugin, with a limited set of features, aimed at being useful while under way. It is not possible to download grib files from within OpenCPN. Many external sources for grib files are available on the Internet. Franks-Weather  is a good starting point.
  • To display grib files as an overlay on your normal charts you have to first activate the grib icon
  • Go to find the plugin tab. Click on the Grib plugin, then the "Enable" button. The "Prefence" Button brings up a small dialog.

  • Tick the "Show GRIB Icon" box. Tick the next box as well, unless you are on old hardware. Not ticking the "High Definition Graphics" box can help to speed up the grib display, in such cases.
  • The Next step is to click the icon, which brings up the Grib Display Control. Use the upper part of this window to navigate to, and select your grib files. The grib files will then be appear in the control. See picture above.
  • Click on the ">" in front of the gribfile. The individual forecasts contained in the gribfile, is then displayed under the gribfile heading.
  • Click on one of the forecasts and it will be displayed. When you move the cursor over the grib display, the values for wind etc will be displayed for the cursor position, in the lower part of the "Grib Display Control". Here you can select what grib values to view. Note that not all gribfiles contains wave data.
  • When zoomed in to show just a small area of the chart, there may not be any wind-arrows visible. The relevant data will, however, still be displayed in the grib dialog. To see the wind arrows zoom out to view a larger area.
  • The gribs are only displayed on the charts when the "Grib Display Control" dialog is open.
  • For certain areas gribfiles describing currents are available
  • OpenCPN will display most grib file formats, but as it is a fairly new feature, bug reports are very welcome.

What is a grib file?

  • If you are not familiar with grib weather files, make sure you understand the basics, before you start to use them. It is essential to understand the limitations of weather forecasts in the grib format. It is also worth pointing out that gribs are not reliable near tropical systems, at least not when using gribs based on the very common GFS model.
  • To get started with gribs and to find sources for downloads, check Franks-Weather.
  • A very good book is David Burch: Modern Marine Weather, with a thorough treatment of the subject.
  • A few files including lectures on  tropical weather and gribs are available here.
  • ZyGrib is a free and open-source software(FOSS) dedicated grib viewer. Grib files can be downloaded by ZyGrib and then opened in OpenCPN.