5 sentences

1. 乌云是下雨的征兆。

   wū​yún shì xià​yǔ de zhēng​zhào.

   Dark clouds are a sign of rain.

   Source: Tatoeba

2. 乌云遮掩了月亮。

   wū​yún zhē​yǎn le yuè​liang.

   Dark clouds obscured the moon.

   Source: Dong Chinese Dictionary

3. 浓密的乌云遮住了午后的阳光。

   nóng​mì de wū​yún zhē​zhù le wǔ​hòu de yáng​guāng.

   Thick dark clouds blocked the afternoon sun.

   Source: Dong Chinese Dictionary

4. 原本晴朗的天空骤然变暗，乌云密布。

   yuán​běn qíng​lǎng de tiān​kōng zhòu​rán biàn àn, wū​yún mì​bù.

   The originally clear sky suddenly darkened and became covered with dark clouds.

   Source: Dong Chinese Dictionary

5. 天空中布满了乌云，看样子要下大雨了。

   tiān​kōng zhōng bù​mǎn le wū​yún, kàn​yàng​zi yào xià dà​yǔ le.

   The sky is full of dark clouds; it looks like it's going to rain heavily.

   Source: Dong Chinese Dictionary