I pointed out at the beginning of the talk that this wasn't really supposed to be a facetious question. But it's apparently because of the title of this paper that it's become known as the butterfly effect. A butterfly was chosen as its effect on atmospheric dynamics must surely be small and a tornado was chosen as its meteorological size is about as extreme as one can get. Extremely small perturbations in a system may result in an outcome as large as the difference between a tornado occurring or not occurring. It is an essential characteristic of a chaotic system.
Sensitive dependence is chaos.
When the results of the eleventh iteration were truncated the equations evolved in a much different manner. Actually, the system of equations Lorenz used can also exhibit other types of behavior that are not chaotic. You don't hear about these solutions as most everyone would agree that they couldn't possibly represent any real weather system. Real weather changes. It never settles down and it also never repeats.