It's raining cats and dogs!
(old-fashioned) It's something that you say when it is raining very heavily. It doesn't mean that cats and dogs are falling out the sky!
The origins of the English expression, It's raining cats and dogs, are uncertain, though the most likely source is a satirical poem by Jonathan Swift, A Description of a City Shower, first published in Tatler magazine in 1710. The poem includes the lines "Drown'd Puppies, stinking Sprats, all drench'd in Mud / Dead Cats and Turnip-Tops come tumbling down the Flood."
"The weather was horrible on Saturday. It was raining cats and dogs all day."
"It's really awful weather outside. It's windy and is raining cats and dogs."
Fuente: Phrases.org.uk