Ryan,
Are you wanting to change the wording or not show anything if there aren't any alerts?
To change where it has nothing there go to your AtomFeed-config.php file and look for this line: Around line 99:
$always_show = true; // true=display message if no alerts false=display message only when alert is active
Change that to false and it will not show anything unless there is an alert.
If you want to change the wording itself, look in the AtomFeed.php file around line 501 for this:
array('N'=>'There are no active watches, warnings or advisories', 'C'=>'#333', 'S'=>'13', 'I'=>'')
Only change what is in the single quotes, otherwise you will have a screwed up alert.
Hope that helps,
John