It would seem to me that you underestimate how complex weather systems are.
A farmer who says "when this happened last, the weather did this next" is more likely to be right than the guy who tries to model atmospheric pressure changes in a chaotic system.
Sure, some people rely entirely on models, but good weather forecasting often involves both. How do we know what a strong north-west pressure system will do? The best answer is "what did it do last time" not "lets model it to death."
PS, this is also how medicine works, which has a lot more science in it than weather forcasting -- historical comparison is an incredibly valuable insight in chaotic complex systems.