Thunderstorm Macro

[Ualaa]

I'd like the flexibility to both round-robin (control) or all at once (offensive) Thunderstorm.
The round robin part is easy, but the all at once part I'm not too sure of.

I was thinking something like this:

/cast [mod]Elemental Mastery
/cast [mod]Thunderstorm
/castsequence Thunderstorm,,,,

Do I need semi-colon's after Elemental Mastery or Thunderstorm? Do I need a stopcasting between the two?
Any help is greatly appreciated.

[Carnage]

When i set mine up (havent got around to it yet), im going to use two macros

/castsequence Thunderstorm,,,,

and

/cast elemental mastery
/cast thunderstorm

The first bound to mouse button 5, the latter bound to shift+mousebutton 5 (this should be possible with my logitech mouse software). Im currently only using the first, but after gathering 8 mobs and instantly killing them im definatly going to start using the latter also :)

[pinotnoir]

/cast Elemental Mastery
/stopcasting
/run SetCVar("Sound_EnableSFX","0")
/use 13
/use 14
/run SetCVar("Sound_EnableSFX","1")
/cast Thunderstorm

Thats my macro for a 5x thunderstorm. It cast my trinkets and EM.