My thanks to Chris, NE5V, for writing this excellent tutorial for setting up the weather script.
I am a good programmer, but not much of a documentation writer. :-)
kind regards to all,
Ben, KD8TIG.

The weather_data.php script works as a companion to AutoSky.  It is not a replacement.  It uses AutoSky to obtain any information on warnings in your area. 
Go to www.kd8tig.com/downloads and look for the file:  weather_data.tgz.  Then copy it to a directory on your node.  I used /usr/local/sbin.

A cleaner, and faster way to get this is to ssh into your node, and in the directory of your choice, execute the following command.
wget http://www.kd8tig.com/downloads/weather_data.tgz
Once this command finishes, execute the following:
tar zxvf weather_data.tgz
 
I chose to put the file in /usr/local/sbin
 
The resulting file is weather_data.php
 
If you find that file, you need to make it executable.  To do this type
chmod +x weather_data.php
 If you are not in the directory where the file exists then include the full pathname to the file such as /usr/local/sbin/weather_data.php
At this point, it's a good idea to test the script in case you encounter any problems.  I went to option 9 on the hamvoip menu which is the Bash shell prompt. and ran the script with a radio turned on to see what happened.
Then you can add a function in the [functions stanza located in rpt.conf to call the script.  It could look something like this.
83=cmd,/usr/local/sbin/weather_data
 
 
Once the function is created and files are loaded, go to option 11 on the main menu of the node, which is the asterisk client.
 
Type
Rpt reload
 
This reloads rpt.conf
 
Then, when AutoSky issues a warning, you can press *83 to see what the warning is.  If there are no warnings or watches, invoking the script will report no active watches or warnings.  
 
You can choose any function.  I chose *83 since *81 and *82 are time and weather related.