I think it will be well understood by most native speakers. If you have phrases you like, then enjoy using them :)

Thank you Nathan and Michael! I think it is more British. I suppose "It is pouring" is more common nowadays. I just wondered if it is understood or it sounds weird when I use this phrase. Because I like using idioms in my native language too :)

I can't remember when I last used or heard it :)

I don't use it. I say "it's pouring outside." It is not a common phrase where I'm from. Maybe it's out of date, but maybe another area uses it? I don't know. Most English speakers know what it means or at the chance they don't they could probably guess.