In a chaotic system, one can distinguish the parameters of predicted outcomes, but cannot predict what will happen within these parameters. This introduces the concepts of weather and climate.
Climate refers to the long-term, generalized conditions expected in a large geographical area. It is the parameters of the chaotic system. Climate can be predicted centuries in advance.
Weather refers to short-term local conditions. This is what is expected to happen within the parameters of the chaotic system. It is highly variable and can only be accurately predicted a maximum of two weeks in advance (due to the increasing divergence of the outcomes in the chaotic model, as the number of time steps increase).
Jon sent me a very funny video on this:
http://www.youtube.com/watch?v=g-F8EO3qOVk