I'm no expert, but my understanding is that weather is the result of the fact that the Earth, and its airy surroundings, spin, and are (more or less spherical). Since it takes longer to go around a larger diameter than a smaller one, the air doesn't all spin as a mass, causing turbulence. Add differing amounts of heat at different places (inevitable if only because the surface isn't at a uniform distance from the sun, and a goodly chunk is at any given time faced away from the sun), and large masses of water, and you get weather.

Maybe this is just the simplistic view I got at school, but I don't recall magnetism getting a look in.

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It is hard to convey five-dimensional ideas in a language evolved to scream defiance at the monkeys in the next tree. -- The Science of Discworld III: Darwin's Watch, by Terry Pratchett, Ian Stewart & Jack Cohen