Board Thread:General Discussion/@comment-73.213.242.57-20150303183113/@comment-24533468-20150304133119

You will need a rapid state of combustion for a fireball to occur, so you must either be able to heat things up to an intense temperature or compress oxygen particles in the air. If you can do either or both, then it's possible. Pyrokinesis is mainly making fire and controlling fire, so yes, it is visible.