It can also refer to breaks in cloud cover, which lead astronomers into trying to make observations, only to have the cloud close in again.
"Sucker hole" is also a term in aviation, which refers to a smaller form of the same phenomenon, but with the observer (the pilot) above the hole instead of below, and implying that the pilot wishes to fly through the hole. It is a very dangerous situation because the pilot cannot tell from above how deep the hole is, and indeed the hole may go all the way to the ground leaving the pilot no way to climb out of the hole once the decision has been made to fly into the hole.
- What Is A Sucker Hole? by Steve Pool, September 18, 2003.