浓云密布nóng yún mì bù

dense clouds gather;overcast with heavy clouds
❍ 须叟，～，一阵大雨过了。(《儒林外史》3) Suddenly dense clouds gathered,and there was a heavy shower of rain.

浓云密布nónɡ yún mì bù

形容天空的云彩非常多。dense clouds gathered, overcast with heavy clouds, Thick clouds overcast the whole sky.