Idiom: The calm before the storm
Example 1: It was just before the department store was to open on "Black ," the biggest shopping day of the year. The store was very quiet, but the sales clerks knew this was just the calm before the storm. As soon as the doors open, there will be hundreds of customers rushing in to try to grab the best merchandise.
Example 2: The sky was dark full of clouds. The weather report said there was a big rainstorm on its way. The calm before the storm lasted only a short while. In just a few minutes, thunder, lightning, and strong winds began to rattle the small village.
Meaning: The calm before the storm can be used figuratively (as in Example 1) or literally (as in Example 2). This expression describes a period of quiet and calmness before an anticipated period of exciting or chaos.