Originally Posted by
Gradius
First off, it's spelled "Psi Storm" not "Sigh Storm".
Psi Storm is only ineffective if your opponent moves out of the way. You have to trap your opponent by either:
1) Going on the offensive, so that your opponent's back is against the wall and that retreat is not an option. Works perfectly against people who camp their army in their natural expo or somesuch.
2) Trap with Force Fields.
3) Flank.
Psi Storm also has critical mass. If you saturate the battlefield with enough psi storms at the same time then your opponent's army will get hit no matter which way he tries to run, especially in SC2 where units clump up more.
But from what I hear, it's apparently more cost-effective to make Colossi for your ground-damage-dealing.