The phrase 'When It Rains, It Pours' is used when something hasn’t happened in quite a while, and then begins happening in large amounts.
Example of Use: “We’ve had more customers today than we’ve had in a month.” Answer: “When it rains, it pours.”
Interesting fact about When It Rains, It Pours
The term 'when it rains, it pours' comes from a common weather phenomenon in which, after there has been no rain in a long time, a lot of rain suddenly falls at once and the weather remains rainy for a while.
