Definition & Meaning of "cold day in hell"

What is the origin of the idiom "a cold day in hell" and when to use it?

The phrase "a cold day in hell" is an idiom used to express that something is extremely unlikely or improbable. While its precise origin is not documented, it has been in use since at least the early 20th century and is derived from the feelings of skepticism, doubt, or a sense of improbability.