GRIB Weather Files—You Gotta See The Rain

Not a good idea to miss seeing the two fronts highlighted by the red ovals.

There are endless debates on forums about which is the best GRIB viewer. These discussions typically focus on which one of the contenders has the slickest features and/or the coolest display of the data.

But you know what? If we really want to clearly understand the weather that’s coming to a place near us, and particularly to avoid, or at least be ready for, violent weather, none of that matters.

Rather, the most important feature that a GRIB viewer should have is the capability to display these three data sets:

  • barometric pressure,
  • wind,
  • precipitation,


The key point is that most GRIB viewers will display all three, but only a few can display the critical three at the same time.

(It’s also good if we can add wave height, as I have done on the screen above.)

Why It Matters

Most really dangerous weather, like violent thunder storms or sudden shifts in wind direction and/or increases in velocity, occur in fronts.

Or, to put it another way, this is the part of a weather system where sudden changes happen that can cause stuff like masts doing centreboard impressions.

And the huge weakness of GRIB files is that they don’t show fronts.

But if we overlay expected precipitation over wind and pressure, apply a little basic weather understanding and practice a little, we can become adept at recognizing fronts.

However, this only works well if we can see all three data sets at the same time. Flicking back and forth does not work very well.

Still The One

This basic requirement is why, despite having looked at several newer and slicker-looking GRIB viewers lately:

  • I still like my good old friend Viewfax from the fine folks over at Sailmail.
  • And for those of you with tablets, PocketGrib works well and can overlay all the variables on one screen too.

Just another example of the importance of not mistaking sizzle for sausage.

By the way, even if we use a GRIB viewer with the above capabilities, it’s still well worth getting traditional weather maps that show fronts, either by SSB-Weatherfax or over satphone, to sanity check our analysis of frontal positions on the GRIBs.

Here’s the map for the same time as the above GRIB:

Of course that begs the question: why bother to look for fronts on GRIBs if weather maps show them clearly? Three reasons:

  • Most weather maps only extend out 96 hours from forecast time, whereas GRIB files go out for weeks, and modern models are amazingly useful for looking at weather out as much as 10 days from forecast time.
  • GRIBs provide a prediction for every three hours rather than every 24 as is common with weather maps.
  • GRIBs provide a much higher level of detail than weather maps.

More Coming

I will be taking a fresh look at all things weather over the course of our cruise this summer.


What’s your favourite GRIB viewer, and why do you like it? And further, has anyone found a viewer for Mac that has the above capabilities? Please leave a comment.

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