As I understand it, Begin Alt. and End Alt. set the minimum and maximum altitude for the selected cloud front. At least that is what I have been using as the definition.
Fade time, is the amount of time set to fade the cloud front out at the end of its life span. Remember you can set the up time and down time of a front.
Some one with more experience with the Cloud may correct me lol.
Hope your working on getting another of your maps up.