What does "a snowball's chance in hell" mean — and why is it funny?

informal

Meaning

No chance at all; absolutely no hope of success.

Where it comes from

An American expression playing on the obvious fate of a snowball somewhere famously, eternally hot.

Why it is funny

The humor is the doomed little hero of the image. You picture one small, hopeful snowball placed in the worst possible spot, melting on arrival — and that is the exact size of your odds.

Used in a sentence

"With no experience, he hasn't a snowball's chance in hell of getting that job."