Dynamic weather engine

I use the default weather generator in fs because I don't have active sky, I know I should get it, but with fs10 coming I might wait. I do by the way have FS Skyworld 2004. I set the slider to minor to moderate changes or none. But anyway heres my problem:I can set clouds either globally or regionally the clouds after awhile start to disipate. I would like to set an area using the regional weather and set the radio stations for a few cumulus clouds and cirus to build into massive thunderstorms covering a wider area. What ingrediants do I need to set in the weather like dew point, temperature pressure, etc. to have this happen? It has been a problem for ever since I bought the program back in 2003 and I haven't posted this, I was just kinda mystified by this though. With the randam weather engine what ingrediants create the cumulus or stratus clouds?Any info would be appreciated.Thank You,Kurt.