hailstorm no
When something happens totally randomly, but everyone does it at the same time, like a bunch of fools decided to be synchronized without even talking.
The whole class stood up at the same time when the teacher said 'sit down.' It was like a hailstorm no moment.
We all screamed 'hello' at the same time without planning. It was a hailstorm no.
They all started singing the same song without any clue. Total hailstorm no.