1、The dark thunderclouds gathered overhead, threatening to release a torrential downpour.
黑暗的雷云聚集在头顶上方，威胁着要释放一场倾盆大雨。

2、When the thunderclouds roll in, it's best to seek shelter and stay indoors until the storm passes.
当雷云滚滚而来时，最好寻找避雨处并待在室内，直到暴风雨过去。