“浓云密布的”可以翻译为“thickly clouded” 或 “heavy with clouds”。
“thickly clouded” 侧重于描述云层浓厚、密集的状态。
“heavy with clouds” 形象地表达出天空被浓云所覆盖、充满浓云的景象 。
例如：
The sky was thickly clouded.（天空浓云密布 。）
The sky was heavy with clouds, looking as if it might rain at any moment.（天空浓云密布，看起来随时可能下雨 。）