据说有一天朱诺看到天空突然乌云密布，就料想这一定是她丈夫兴起一团云来遮盖自己的放荡勾当。 It is said that Juno one day, perceiving the skies suddenly overcast, surmised that her husband had raised a cloud to hide some escapade.
乌云密布，大雨就要来临。 Dark clouds were gathering in the sky. Heavy rain would come soon.
乌云密布预示着将要下雨。 The black clouds threatened rain.
天空乌云密布，我们看得出快下雨了。 The sky clouded over: we could see it was going to rain.
