refers to the circumstance
It is "IT".. INFORMATION TECHNOLOGY is raining
it = water
If you remembered your Earth Science, you wouldn't be asking that, silly.
It is the weather.
No. Rain is part of weather. So is snow and all the other conditions that make the weather. My mom use to ask what's it doing out there. I'd say it's freezing and dad would say then bring it in and warm it up.
I didn't understand a word of *it*