system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does the sky turn green when a tornado is about to happen?
gpt
I actually looked this up once since a coworker got me thinking. 

And yeah, it's not just a tornado thing. It's the red sunlight from a sunset going through the stormcloud, which being water, will filter blue, and give you the green.  

So big cloud, like a storm that would produce tornados + red light, like sunrise or sunset, will result in green light.