Thunderstorm

[LavCat]

I started using Thunderstorm last week for the first time ever. As I have read, the rate seems to increase with level. Does anyone know the rate at, say, level 20? And what is the range? Does the range increase any with skill level, or is the range fixed?

Thanks in advance!

(The unasked question is why at level 12 does Thunderstorm not kill anything in hell? -- even with maxed lightning mastery.)