Complex sentence: Had the butterfly not flapped its wings, the trajectory of the system might have been vastly different-it's possible that the set of conditions without the butterfly flapping its wings is the set that leads to a tornado.
Split into simpler sentences: Had the butterfly not flapped its wings, the trajectory of the system might have been vastly different. It's possible that the set of conditions without the butterfly flapping its wings is the set that leads to a tornado.