Marine Data Literacy 2.0

Providing instruction for managing, converting, analyzing and displaying oceanographic station data, marine meteorological data, GIS-compatible marine and coastal data or model simulations, and mapped remote sensing imagery





Home > 9. Operational/Synoptic > 9.13 GFS Meteo

9.13 Visualizing Modeled Meteorological Products in IDV: GFS

  • Exercise Title:  Visualizing Modeled Meteorological Products in Integrated Data Viewer (IDV): Global Forecast System (GFS)

  • Abstract:  The Global Forecast System (GFS) products are arguably the most widely used meteorological simulations, due to their ease of access (through full OPeNDAP compatibility) and the fact that no fees, licenses or registrations are required.  The results are currently available only in GRIB, but IDV and Panoply can easily manage to display these results.  Below, you'll work with a typical scalar quantity (surface temperature) and a typical vector quantity (surface wind vectors).  THIS LESSON IS PROVIDED FOR EDUCATIONAL PURPOSES ONLY.  DO NOT RELY ON THESE PRODUCTS FOR NAVIGATION, FORECASTING OR FOR ANY OPERATIONAL PURPOSES AT SEA.

  • Preliminary Reading (in OceanTeacher, unless otherwise indicated):

  • Required Software:

    • IDV - Latest version, set up according to 9.1

  • Other Resources: 

  • Author:  Murray Brown with big help from Rich Signell

  • Version:  1-22-2015

1.  Some users may encounter problems loading these products at the ADD SOURCE stage (see below).  Be aware that a few very large data catalogs (e.g. HYCOM) take a long time to load, especially if you have not selected data subsets by geography (REGION), time, depths or heights (LEVELS) or data density (STRIDE).
2.  Open the main GFS website to read more about this major modeling system.  It is possibly the most widely used metocean model in the world.
3.  The best place to get all the data, including a new 0.25-degree version, at the NOMADS site.  Open that link and read more about all the many datasets you can find there.
4.  If you scroll down the page, you'll find these major sections (collapsed here for clarity).
Data Set freq grib filter http gds-alt
Global Models
Regional Models
Ocean Models
External Models
5.  Now let's look at the GLOBAL MODELS, as you see here.  For most of the models, there are 4 links to see more information.

Pick any model and look at the 4 available sub-pages, to see what's there.

6.  Find the 0.25-DEGREE products for GFS, and click on the OPENDAP-ALT link.  Somewhere in here are the links you need to hook up these data with IDV.

The folder seems to have a "rolling" set of folders from 10 days previously to today (for the author writing this exercise).

7.  Click on the DIR link by the last day.  This directory of data products opens.  There are products of 2 kinds stored here:
  • Single time products, with ANALYSIS AT in the file title
  • 10-day products, with STARTING FROM in the file title

Looking closely at the descriptions, we can see the products are produced at times 00H, 06H, 12H and (presumably) 18H every day.  But actually, as you'll see below, the complete product set includes 3-hourly files.

8.  For the 5th listed product, a 10-day aggregate, click on the INFO link to see this typical listing of metadata.  [The 165 variables that follow this segment have been omitted for clarity.]

The URL you need for working in IDV is the first item below the horizontal line:  DATA URL.  Copy and save it, because we'll need it soon

9.  If you open the 6th link above, for the single-time product, this is what you'll see.  You can save this URL also

10.  And here are our two saved URLs, ready to use in IDV:
  • Ten days, Jan 20-Jan 30, 2015:
  • One day, Jan 20, 2015
11.  Run IDV.  Make sure it's the latest version, properly set up with Exercise 9.1

12.  On the dashboard panel, select FILE > DATA CHOOSERS > GENERAL > URL.  Then enter the 10-day URL you just found above.  Then click ADD SOURCE.


13.  Very quickly, you'll see these 2 categories of FIELDS added.
  • 3D GRID - parameters that vary with height and are provided layer-wise within multidimensional grids
  • 2D GRID - parameters given for a single specific height, provided in separate grids

The 3D group is quite modest

14.  The 2D group is huge, including many near-surface variables that are critical for weather and climate modeling.
15.  Before we do anything else, we need to reduce the total possible dataset by subsetting it in space and time.  Otherwise our IDV installation will get bogged down with huge file downloads, etc. etc.  So don't select any variable now.
16.  Right-click on the 0p5 object, and select PROPERTIES.

NOTE:  0p5 is the new, best way to specify "0.5" in a filename.

17.  This subsetting window opens, with 5 different tabs, as you see here.
  • TIMES - Look closely and you'll see that they are actually 3 hours apart.  We usually do not select times here, so leave these alone.
18.  Now we need to do something about the location.  Select this tab:
  • SPATIAL SUBSET:  We need to select the Liberia area of interest.
19.  Draw a small rectangle anywhere on your map.  This activates the BOUNDING BOX widget.
20.  Now enter the correct coordinates for Liberia in the BOX.

You can click APPLY now.

21.  Now you can select the DISPLAY for the data (i.e. the type of map), and other possibilities:
  • Pick TIMES > USE SELECTED and then select the very latest grid
  • REGION is always selected in the upper-left PROPERTIES box, never in the lower-right box, so ignore it here
  • STRIDE can be ignored here; we'll use it later in this exercise


22.  This map of surface air temperature appears.  You can see the date and time just above it, as either a series or a single point.  The color palette information in the right margin.

23.  The default palette usually isn't a good choice, so you can click on the palette in the right margin to get these controls for it.

The RADAR > DBZ choice is usually good, because it is the standard rainbow.

24.  Here's the result of that choice.  The figure is much more interesting and informative.  The Current Atlases may give you some inspiration to try to explain it, because SST is sometimes closely related to circulation systems.

25.  Now we'll make some wind vectors and add these to the same map.  In the upper left corner find DATA SOURCES > FORMULAS and click it to open a long list of things you can calculate from the data already loaded.  Find and select MAKE FLOW VECTORS FROM U AND V DATA.

26.  This new windows opens, asking you to identify specifically which grids are the U (left side) and V (right side) components to use in the formula.
27.  Open the U menu of choices, and find the U component in the 3D group of grids.

Just below it, you can see you now have TIMES choices.  Leave them at USE DEFAULT (i.e. use all times)

28.  Select the LEVEL tab and then choose 1000 millibar.  Essentially that means 1 bar, or very near the surface.
29.  Select the REGION tab to confirm visually that you are still focusing only on Liberia.
30.  Select the STRIDE tab to select a method to thin the data.  Select EVERY THIRD POINT, which gives you only 1/9 of the data, i.e. 1/3 times 1/3.
31.  On the V side, make all the same choices, exactly.


32.  Then click OK at the bottom of the UV selections window.

33.  After a few moments of calculating, something similar to this nice wind map appears (depending on the STRIDE you used).  Notice the control for the times appears to be a solid green bar, because it has so many individual times available.  Click at several points to see the map change over time.

34.  Now, you should go back to the stage where you specified the wind vectors, and experiment with the various controls so you get the best figure for your purposes.  You can change the size the arrows, their spacing (with STRIDE), color, etc.  Anything you don't like can be changed.
35.  If you want to make an animation, then select VIEW > CAPTURE > MOVIE and experiment with the possibilities.

HINT:  Select GIF for the output to get the smallest product file.

36.  Here is the author's attempt at a movie of the data above.  When you view it at full scale, the arrows are not pixilated, so don't worry about that.
37.  Make sure to save your work.  The full IDV map with all settings, can be saved with FILE > SAVE AS in the folder PRODUCTS > IDV > PROJECTS with the extension XIDV.  the movie can be saved there or in the folder PRODUCTS > IDV > ANIMATIONS.