表达 “a cold snap” 通常被用来描述 “温暖天气后出现的一段短暂的寒冷天气”。这种天气可能来得很突然。与 “a cold snap” 同义的另一个表达是 “a cold spell”。

例句
There was a cold snap at the start of the year.
今年年初有一股寒流。

The weather had been perfect for growing food, but the sudden cold snap threatened the crops.
当时的天气本来非常适合种植粮食，但突如其来的寒流却危害到了庄稼。

The weather forecaster said that a cold snap is heading our way, so we should probably postpone our holiday.
天气预报员说有一股寒流正向我们袭来，所以我们或许应该推迟度假安排。