Instant, 1RR (3) Lightning Storm deals X damage to target creature or player, where X is 3 plus the number of charge counters on it. Discard a land card: Put two charge counters on Lightning Storm. You may choose a new target for it. Any player may play this ability but only if Lightning Storm is on the stack.1
Illus. Luca Zontini
When you play this card, you immediately have a chance to play its ability since you'll have priority. If you don't, and all other players pass, the spell will resolve. You won't receive priority again -- and thus won't get another chance to play its ability -- unless someone else plays this card's activated ability or some other spell or ability. [Coldsnap FAQ 2006/06/14]
If there are no legal targets to choose, then you cannot change the target. [Coldsnap FAQ 2006/06/14]
The charge counters go away when this card leaves the stack. [Coldsnap FAQ 2006/06/14]
Coldsnap
(Uncommon)