It’s chucking it down
Definition 1 of 1
Pro Tip 1/3Very Informal
Used mostly in casual conversations among friends or in informal settings. 
I was going to walk to the market, but it's chucking it down, so I'll drive instead.
Pro Tip 2/3British Slang
It's a British English slang term, not commonly used in American or other types of English. 
I heard it's chucking it down in London today.
Pro Tip 3/3Weather Context
Use it when discussing the weather, specifically when it's raining a lot and suddenly. 
As soon as I stepped out, it started chucking it down.