Go to the dataset list
Expand NOAA - National Climatic Data Center (NCDC)
Select AWIPS Eta Model Data to the retrieve panel
Drill down the directories to /200401/20040108
Select (single-click) the file early-eta_212_20040108_0000_fff
discussion:
These weather datasets can be complicated. We need an introduction to the data. Here's an easy way to get it: notice that when you selected the file the full URL to that resource appeared in the location bar. It should read:
http://nomads.ncdc.noaa.gov:9090/dods/NCDC_NOAAPort_ETA/200401/20040108/early-eta_211_20040108_0000_fff
This URL points to an OPeNDAP server (aka DODS), but it's a good guess that the machine and domain have introductory materials. Copy and paste the first part of the URL (http://nomads.ncdc.noaa.gov) into a browser. Bingo! The host has a full set of web documents describing the web resource which you can research to find out what the data means. Now, armed with this information, we can continue.
Double-click the file to see it's structure
Check "Show Descriptions"
[this will give use more information on the fields in the data]
Choose the grid named "cpofpsfc" (select the grid and array variable cpofpsfc)
[according to the description this is surface probability of frozen precipitation, ie snow]
Output to plotter
Turn on coastline
Plot it
The results should look something like this:
discussion:
Besides adding nice text labeling there is another thing we can do to improve the plot. Notice that the ODC has automatically determined missing values to be -9.99E33, 0, and 100. If you look back at the data description on the retrieve panel you can see it only lists the -9.99E33 which it calls a "fill value". The reason why the ODC has also identified 0 and 100 is that they have solid continuous areas that cause value spikes in the data. The ODC tends to regard these kind of spikes as likely missing values. We can improve our plot by making dedicated colors for these special values.
Add Colors for Key Values:
Go to the Colors tab
Click "Plot Uses"
[the color editor will become active]
Select the Missing range
Edit the missing values text box in the range editor (middle of screen) by deleting 0 and 100
Press enter to save your changes
[notice how the range list updates to reflect your change]
Add a new range (add range button is in lower left corner)
Select the new range
[notice that an interface to modify the range appears in the range editor]
Change "Single Value" to "Yes"
Change the data value to 100
Change the color to a slightly dark green (I used 47 FF D0 )
Repeat for the 0 value but used a washed out, low-saturation, yellow (29 50 FF)
[coloring the 0 value will show us the satellite swath]
Modifying the Text:
Go to the Plot Options tab
Turn off "Generate Axis Captions"
Add the new title, date and axes captions
Animate the Plot:
Go to the Variables tab
Change the Time constraint from "1" to "1-17"
Plot it
[you are watching the snow pattern over a 17-hour period on January 8, 2004]
[tip: if your image size is too large you could run out of memory doing this]
Tip: Finding More Data
The dataset list only lists some of the data available at NCDC. Explore there to find more OPeNDAP data sets.
OPeNDAP Data Connector Plot Gallery ·
Revised 25 January 2004 ·