Some people say that it is correct to say "The rain is heavy" not "The rain is big."
Thanks for your help.
The raindrops might be big.
There are tons of ways of saying it colloquially, e.g. it's chucking it down, it's pissing down, it's bucketing down. It probably depends which country you come from!
One of my favourite metaphors for torrential rain is 'It's coming down in/like stair-rods - yet another metaphor that refers to old technology: http://www.walton-rugs.co.uk/images/..._lifestyle.jpg . I wouldn't say they're extinct (yet), but the last time I lived in a house with a stair-carpet held down in this way was a good 50 years ago.
I use "coming down in stair-rods" a lot!
Does it rain cats and dogs in the UK?
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.