Lab 4 Handout - Marrella

Note that the yyyymmdd/tttt tells the user from which model run the data are derived, or, in other
words, what day and time the model was initialized. The FTTT tells the user the forecast hour from
this model run. For example, 20091022/1200F012 would be the 12­hour forecast from the 1200 UTC
22 October 2009 model run, valid at 0000 UTC 23 October 2009. As such, not all the times listed
correspond to the same model run. Generally, you will want to use the most recent data available
(found at the bottom of the list).
Let’s try plotting geopotential height and absolute vorticity at 500 hPa using the 24­hour forecast
from the 1200 UTC 22 October 2009 Eta/NAM model run. Be sure to select the appropriate time,
pressure coordinate, level, correct functions, etc. You can always adjust the contour interval and
contour properties of the variables being plotted by selecting more on the lower right of the Model
Plan View box. Once you get the heights to plot overlay the absolute vorticity. See if you can get the
absolute vorticity to appear with color filling instead of contours.
NOTE: In GARP, it is easy to clear a variable that you plotted without clearing the entire screen.
Simply go to the bottom of the graphics window and single click the left mouse button on the title of
the variable you want taken off the screen. The title text will turn gray. You can bring the variable
back up onto the screen with a single click of the left mouse button on the grayed­out title.
FURTHER NOTE: In addition to selecting the already defined variables and functions, one can manually
enter a gfunc or gvect in the bottom part of the Model Plan View window.
Click ICON 9 to clear the graphics screen. Your plot should be cleared with only the background
map remaining.
3
LOOPING WITH GARP
In GARP, we can easily loop through a series of images, even with multiple overlays. We will now
make a loop of the visible satellite imagery with surface observations overlain. Use the Northeast
United States as the map background.
Click on the satellite and radar icon (ICON 1).
Select GOES­8 (this is actually GOES­12 data), 4 km, and VIS.
Click and hold the left mouse button on 20091022/1315 and drag down to the most recent time.
There should be about 7 forecast times highlighted.
Click the “Display and Close” button. You should see a series of satellite images plotted on the
screen.
Since we want to display surface observations taken around the same time the satellite pictures
were, we should use the “Time Matching” feature of GARP. In the Time menu, select Time
Matching, and then select Closest Time Match.
To overlay the surface obs, select ICON 2. Click Multi­color. Notice that the proper times are
already selected to match the satellite.