Region: US | Usage example: We stayed inside because it was raining harder than a cow wetting on a flat rock.

It's raining harder than a cow wetting on a flat rock

Meaning

It is pouring rain.

Describes torrential downpours.

Origin notes can vary by region and source; this page gives the commonly reported explanation and usage context.

Rustic American expression drawing on the slow process of a cow urinating on a rock.

Heard in Southern US speech in the early 20th century.