2 sentences

1. 彤云密布，预示着大雪将至。

   tóng yún mì​bù, yù​shì zhe dà​xuě jiāng zhì.

   Dark red clouds are gathering, indicating that heavy snow is on the way.

   Source: Dong Chinese Dictionary

2. 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