One thing you could do is to change your NWSforecastScript.php5 near the top from <?php
// error_reporting(E_ALL);
to <?php
error_reporting(E_ALL);
ini_set("display_errors","1");
so we can see what PHP is really griping about to blow up with a 500-Server Error.
Since you aren't running my template set, my diagnostic ability on your site is limited.