3 sentences

1. 天有不测风云，人有旦夕祸福。

   tiān yǒu bù​cè fēng​yún, rén yǒu dàn​xī​huò​fú.

   Fortune is as unpredictable as the weather, and life is full of unexpected turns.

   Source: Dong Chinese Dictionary

2. 山顶上风云变幻，我们必须在暴雨前赶快下山。

   shān​dǐng shàng fēng​yún biàn​huàn, wǒ​men bì​xū zài bào​yǔ qián gǎn​kuài xià​shān.

   The weather on the mountain top is changing rapidly; we must descend quickly before the rainstorm.

   Source: Dong Chinese Dictionary

3. 国际风云变幻莫测。

   guó​jì fēng​yún biàn​huàn​mò​cè.

   The international situation is unpredictable.

   Source: Dong Chinese Dictionary