SCoates wrote:A snowball is already frozen over. It would have to either be water freezing over, or snow not melting very quickly in hell to be impressive.

I sometimes write with imprecision (as others have pointed out), but usually with humorous intent (which is not always recognised).
Here, I deliberately mixed two well-known phrases; "not a snowball's chance in hell" and "when hell freezes over".
A snowball has to be slightly unfrozen (by the pressure of the maker's hands) to be compacted and thereafter may remain partially unfrozen or may re-freeze, dependent upon the ambient temperature, I think. :wink: