When a Hard Rain's a Falling

Today it rained all day. At one point it was raining so hard I heard from the outer office, "It's raining cats and dogs". Made me think of what my dad, Joe, would say when it looked like a hard rain was a coming.

"It's gonna rain like a cow pissing on a flat rock."

Being a kid, I asked what that meant. He replied, "ever see a cow piss on a flat rock?"