Keep in mind that for advforecast2.php to work correctly, the URL-path and Filesystem-path need to match. That is:
advforecast2.php
DualImage.php
./forecast/images/*
./forecast/icon-templates/*
need to have that filesystem and URL-path setup to operate properly. By 'match' I mean that
http://your.website.com/ maps to /home/somepath/httpdocs
http://your.website.com/forecast/images/skc.jpg maps to /home/somepath/httpdocs/forecast/images/skc.jpg
etc. WordPress does funny internal mapping so the URL-path and filesystem path for the real file don't always match and that breaks the script.
Oh, and don't change the internal addressing in advforecast2.php from relative filesystem addressing (./forecast/images) to URL addressing (https://...) -- it will break the script in other ways.