Seasons, Island Living, and terrible snow storms in Sulani

I wonder if it could be the fact you change weather every time you change the world. Does that mean when you move a sim into another world (the same world you are playing in) or does that mean you start a "new game"?

I would suggest you "repair" your game and see if that fixes it. I know when they release a pack or patch, it seems to mess up a lot of things when playing saved saves.