我々が静かに夕食をとっていると、突然、母がもう一度学校に行くつもりだと言い出した。

We were having a quiet supper when out of the blue my mother announced she was going back to school.

突然、明かりが消えた。

All at once the lights went out.

突然、空が曇ってきた。

All of a sudden, it became cloudy.