to cloud over

1.乌云密布
2.满脸愁容

1. To become filled with clouds. (NOTE used to describe a sky)
2. To become sad or discouraged in appearance. (NOTE used to describe a face)

例句
1.This morning the weather was beautiful but this afternoon it started to cloud over, and I think it will rain tonight.
今天上午天气很好，但下午乌云密布，我想今晚要下雨。

2.At first my brother was happy to see me, but when I told him the bad news about our mother his face began to cloud over.
一开始，我兄弟见到我很高兴，但当我告诉他母亲的坏消息时，他开始满脸愁云。