SOLVED. Group of young adults with powers including a clairvoyant comedian [s]

[Lobstergirl, au gratin]

Peppermental, are you still looking for this or did you find it?

[Martin]

Scorpion Shards. One of the main characters can predict the future by knowing the exact effect of a cause. Kind of like the butterfly effect. I don't remember if he was funny or not

[Bargle]

Peppermental wrote: "Read it in 8th grade (≈2008) so I think it's a YA book with a generic title and cover. There was a group of people with varying powers and the one detail stuck in my mind is that one was a guy who ..."

This is definitely True Talents by David Lubar. I read it recently and it matches all your points except that the large city is Philadelphia.

[Bargle]

I've sent a PM to Peppermental.

[Bargle]

No reply from Peppermental, but I'm sure "True Talents" is the correct answer, so a Mod can move this to solved if they like.

Note to self: correct answer.

[Lobstergirl, au gratin]

Okey.