乌云是下雨的明显先兆。

Black clouds are an unmistakable sign of coming rain.

乌云中电光闪闪。

The lightning flashed out from the black clouds.

天空中乌云密布。

The sky was full of dark masses of clouds.

天空中的乌云预示暴风雨即将来临。

The dark clouds in the sky meant that a storm was coming.

天上乌云密布，预示就要下雨。

There were dark clouds overhead promising rain.

乌云滚滚，山雨欲来，革命即将爆发。

The storm clouds of revolution were gathering.

天空乌云密布，阴沉沉的。

The sky was dark and threatening.

天边乌云密布。

Dark clouds massed on the horizon.

暴风雨乌云正在聚集。

The storm clouds were gathering.

乌云密布预示大雨将至。

The clouds threatened rain.

乌云渐渐散开，露出了蓝天，这和她的情绪形成了鲜明的对照。

In sharp contrast to her mood, the clouds were breaking up to reveal a blue sky.

天空中乌云黑沉沉地压下来，发出隆隆声和噼啪声。

The sky, swollen like a black bladder, rumbled and crackled