meaning: it is raining very hard.
This expression comes from Old England when houses had thatched roofs (made of grass).
The dogs and cats used to sleep on the roof, and when it rained, they would slide down onto the ground.
This blog is mainly to explain a different English language expression every day. Sometimes I post other stuff. I also have a YouTube channel which is mostly about computer software: https://www.youtube.com/englishspacedog
