McIDAS-X Learning Guide
Version 2020

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Grids and Grid Files - Displaying Gridded Data

In this exercise, you will use the GRDDISP command to display grids. GRDDISP can be used to draw contours, streamlines, or plots of grid data.
  1. Show frame 4, and display the first GOES-16 0.5km Visible image centered on Washington DC. Add a high resolution map.
    Type:  SF 4;IMGDISP ABI/CONUS.1 4 STA=DCA BAND=2 MAG=-8;MAP H
  2. Contour the divergence grid created in the previous lesson over the satellite image with a contour interval of 5 and graphics color level 3. Because the values of divergence are small, use the POWER keyword to scale the values. Make the convergence (negative divergence) areas dashed. Use NAV=C to use the navigation in the current frame.
    Type:  GRDDISP TG.2 PARAM=DVG NAV=C CINT=5 COLOR=3 POWER=6 DASH=NEG
  3. Contour the temperature advection grid over the image using a contour interval of five degrees per sec scaled by 10**5. Make negative values (cold air advection) dashed.
    Type:  GRDDISP TG.2 PARAM=TADV NAV=C CINT=5 POWER=5 DASH=NEG
  4. For the following exercises, you can use RTGRIDS/GFS to create a McIDAS grid, but grid availability changes, so we've created a reliable McIDAS Grid file to download from a FTP site to use for the following exercises. For this example, the GRID4002 file must be placed in the directory <local-path>/mcidas/data directory. (This will be the same directory where GRID4000 and GRID4001 from previous exercises have be written.)
    Download the file from ftp.ssec.wisc.edu.
    ftp ftp.ssec.wisc.edu
    login anonymous
    prompt
    binary
    cd pub/mug/Data/Grid
    get GRID4002
  5. Create a plot on frame 1 of the 24 hour 700 mb height forecast over the U.S. from the model run in the local TG.3 dataset. Use a label size of six pixels, a 60 m contour interval and label every other contour. Switch to the frame after plotting. Note: To create your own grid file from current data, run the command: GRDCOPY RTGRIDS/GFS TG.3 DAY=#Y TIME=0 FHOUR=0 6 12 24 GPRO=MERC NUM=ALL DEL=YES
    Type:  GRDDISP TG.3 FHOUR=24 LEV=700 PARAM=Z MAP=USA PRO=MERC GRA=1 LSIZE=6 CINT=60 LINT=2 SF=YES
  6. Overlay the 500 mb temperatures in degrees C in yellow. Dash the contours and use a label size of six pixels and a contour interval of 5.
    Type:  GRDDISP TG.3 FHOUR=24 LEV=500 PARAM=T UNIT=C NAV=C LSIZE=6 COLOR=3 CINT=5 DASH=ALL
  7. Create a plot of wind barbs over the US at the 250 mb level using the TG.3 dataset. Draw the barbs in yellow with a size of 12 on frame 2 and show the frame after the plotting is complete.
    Type:  GRDDISP TG.3 FHOUR=24 LEV=250 PARAM=WINDB MAP=USA LSIZE=12 COLOR=3 GRA=2 SF=YES
    Notice that the density of the grid points and the size of the wind barbs makes them overlap.

  8. Erase the frame and redo the previous plot, this time plotting only every other grid point.
    Type:  ERASE G;GRDDISP TG.3 FHOUR=24 LEV=250 PARAM=WINDB MAP=USA LSIZE=12 COLOR=3 PINT=2 2
    The PINT keyword can be used to declutter a dense grid plot.

  9. Erase frames 1-4. Create a sequence of the 0, 6, 12, and 24 hour 500 mb height field over the US from the 0Z GFS model run.
    Type:  ERASE F 1 4
    Type:  GRDDISP TG.3 TIME=0 FHOUR=0 6 12 24 LEV=500 PARAM=Z CINT=60 MAP=USA GRA=1 4 LSIZE=6 LINT=2 SF=YES
  10. Set the loop bounds to frames 1-4. Change the dwell rate so it pauses longer on the last frame. Then, start the loop.
    Type:  LS 1-4;DR 3*3 10
    Press:  Alt L
  11. Stop the loop.
    Press:  Alt L

In this exercise, you will display the forecasted sea level pressures for the GFS 0Z model run in TG.3. Then, you will compute the 1000-500 mb thickness for that same time and display the thickness on top of the sea level pressure contours.

  1. List the available sea level pressures from the 0Z model run.
    Type:  GRDLIST TG.3 NUM=ALL PAR=P LEV=MSL
  2. Erase the graphics in the first four frames.
    Type:  ERASE G 1 4
  3. Display the sea level pressure data from the 0Z model run. Plot the contours over a map of the United States.
    Type:  GRDDISP TG.3 FHOUR=24 PAR=P LEV=MSL MAP=USA
  4. Calculate and display the 1000-500 mb thickness for the same forecast time.
    Type:  GRDDISP TG.3 MAP=USA FHOUR=24 MATH='G2-G1' COLOR=3 NEWPAR=THCK GPM G1='LEV 1000;PAR Z' G2='LEV 500'
  5. Exit McIDAS.
    Type:  EXIT

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