YOU SAID:

it's raining cats and dogs outside

INTO JAPANESE

それは、土砂降りの雨外

BACK INTO ENGLISH

It is pouring rain outside.

INTO JAPANESE

それ外は土砂降り。

BACK INTO ENGLISH

It's out of the downpour.

INTO JAPANESE

外大雨です。

BACK INTO ENGLISH

Outside is a heavy rain.

INTO JAPANESE

外は大雨です。

BACK INTO ENGLISH

Outside is a heavy rain.