Final answer:
The phrases 'It's raining cats and dogs outside' and 'It's coming down in buckets outside' are idiomatic expressions used to describe heavy rain.
Step-by-step explanation:
The phrases 'It's raining cats and dogs outside' and 'It's coming down in buckets outside' are both idiomatic expressions used to describe heavy rain. They do not have a literal meaning. Instead, they are used to emphasize the intensity of the rain. These expressions are commonly used in spoken English and informal writing. It's important to note that they are not considered formal language and would not typically be used in academic or professional writing.