Just out of curiosity, why do you need a generator?
Recently, I've been trying to make weather a more significant factor in my campaign, in part to add a sense of veracity and in part to provide another potential tactical factor to my encounters (at least, the outdoor ones) and the heroes' plans.
I thought about some sort of system to generate the weather, but ultimately decided that I didn't need it. I don't use a random generator to come up with my maps; why should I do it for the weather.
I choose the weather (within reasonable expectations) that fits the challenges or atmosphere I want for my story. In the same way that I design a map, pick out opponents, or otherwise set up elements for an encounter or segment of a story.
I recommend that route!