Hi Andrew,
First, thanks for your appreciation... and welcome to the forum!
Then for your question, go to Cumulus Menu Configuration --> Internet --> Files Tab.
Cumulus need 4 infos to know what you want to do :
1 - Local Filename - is to inform Cumulus on where is the file to process, in your Pc. (ie C:Cumulusweb).
2 - Remote filename - is for "whre to put file" on your Web site (ie public_html/weather).
3 - Ftp? - is to say to Cumulus... send it for me!
3 - Process? - is to say to Cumulus that this file contain special words to replace by weather data.
Then I hope having help you,
Jacques