Chuck,
You are missing the noprint parameter. Because you want it to echo(print) $advisory_html here in the output after it has been included and not printed from inside the script.
Also for the 'CSS style switch for no advisory / advisory' to work the divs have to be this way in my example.
Try this:
<div id="content">
<h1 id="pageName">Current Weather Conditions Glendive, Montana</h1>
<div class="story">
<?php
include 'http://www.chucksweather.com/rss-advisory.php?inc=Y&summary=Y&noprint=1&detailpage=NOAA-advisory2.php';
if (preg_match("|There are no active|i",$advisory_html) || preg_match("|Advisory Information Unavailable|i",$advisory_html)) {
echo '<div class="advisoryBoxnoactive">' .$advisory_html .'</div>';
}else{
echo '<div class="advisoryBox">' . $advisory_html .'</div>';
}
?>