Hi Marian,
FWI is a newly calculated item, and won’t show up in older forecasts (not sure if that’s what you’re asking). By the way, WXSIM is calculating Canadian FWI (or a close approximation of it, as the official algorithm is very complicated, especially regarding fuel moisture), Australian FFDI, and then an average, which I think from the reading I’ve done may be the best figure overall. It’s that last one (the average) that is now saved in the .wxf files and can be recalled and graphed in wret.exe. The interpretation of the blended index can be found in manual.doc, in section XVIII. Please let me know if that answers your question!
Tom