calm before the storm, the

calm before the storm

A period of inactivity or tranquility before something chaotic begins. Likened to a literal period of calm before a storm begins. Oh, this is the calm before the storm—the dinner rush will turn this place into a mad house.
See also: before, calm, storm

the calm before the storm

or

the lull before the storm

COMMON You describe a very quiet period as the calm before the storm or the lull before the storm if it is followed by a period of trouble or intense activity. Things are relatively relaxed at the moment, but I think it's probably the calm before the storm. The Emergency Department is fairly quiet, the lull before the storm. Note: This expression can be varied by replacing the storm with another storm or by adding next before storm. The fragile ceasefire may be just the lull before another storm.
See also: before, calm, storm

calm before the storm, the

A sense of foreboding, during a particularly serene period, that violence is on its way. “Fair weather brings on cloudy weather” is an ancient Greek proverb. Numerous writers from approximately 1200 on also are recorded as saying that calm will come after a storm. Transferring fair and foul weather to human affairs, particularly to good fortune and adversity, and to peace and war, are also very old. “It is a common fault of men not to reckon on storms in fair weather,” wrote Machiavelli in The Prince (1513). In modern times the phrase frequently has been applied to an uneasy peacetime, when war seemed imminent. It was so used in the late 1930s, when it was already a cliché.
See also: before, calm