Why does the sky often turn green before a tornado?
We don’t really know. Every time I’ve seen the green sky, it’s been associated with hail. Since most tornadic storms also produce hail, it’s likely we’re seeing something associated with the hail. (I’ve also seen the green color with non-tornadic hailstorms.) Beyond that, it’s hard to say. There has been research into trying to identify why hail makes the storm look green, but it’s not clear what the answer is.
