pissing

(adjective) (slang) raining very heavily

Example Sentences:

A: What do you dislike about Vancouver?
B: It can go from sunny to pissing in five minutes.

It’s pissing outside right now. Do you have an umbrella?

From the Blogs:

Pissing Rain & Howling Wind

Media:

Similar idioms:

1. raining cats and dogs
2. three sheets to the wind
3. pissed off