For WXSim to work properly it needs to download files from the internet as well as using your WD data. Not having a website is not an issue but the PC running WXSim must be connected to the internet. It only really works on your area once Tom (the author) has customised it for your location, once this is done it will work for your area, it’s not really a trial in the normal sense prior to the customisation but just shows you the kind of output and allows comparison with real forecasts for the ATL area.
I’ve been using it for some years now and find it very good.
Stuart