How to install rNOMADS with GRIB file support on Windows

Two years ago, I wrote a software package for R called “rNOMADS” that interfaces with online weather and sea ice model repositories to gather data in real time, for free.  The data are delivered in two ways: a simple, pure R, cross platform interface using GrADS-DODS, and binary files in GRIB format.  The one issue with GRIB is that this format can’t be read directly into R; it requires the external program “wgrib2.”  Installing rNOMADS with GRIB support for Linux is covered in this post (Mac OS is probably similar).  I thought GRIB support for Windows was impossible until the guy who runs this blog casually told me he’d figured it out.  So, I finally got around to trying it myself, and I’m happy to say I got it to work!  Here’s how:

Step 1:

Download the most recent wgrib2.exe version and all DLL files from Wesley Ebisuzaki’s web site:  Click here.

Step 2:

Make a directory somewhere on your computer.   I chose:  C:\Program Files\wgrib2

Copy the .exe and the .dll files to this directory.

Step 3:

Append the directory path to the Windows PATH variable.  Find out how to do this here.

Edit: a user points out that sometimes this doesn’t work.  If not, change the path variable in R using Sys.setenv():

Sys.setenv("PATH" = "C:/Program Files/wgrib2")

 

Step 4:  If R is open, close and reopen it.  Then try the following command in the R interpreter:
system("wgrib2")

If you get a bunch of text that looks like the image below, you’ve succeeded.  You can start reading GRIB files with rNOMADS!

Output of wgrib2 call from R.

Output of wgrib2 call from R.

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