The day dawned sunless and with a low cloud base.

黎明时天气阴沉，云层压得很低。

《柯林斯英汉双解大词典》

The formation of the channel is initiated when electrons surge from the cloud base toward the ground.

当电子从云层底部涌向地面时，通道就开始形成了。

youdao

FYI, one aircraft has landed and reported cloud base 80m, visibility 1km. What is your intention?

通知你，一架飞机降落并报告，云高80米，能见度1公里，你的意图是什么？

youdao

As a parcel of dry air rises, it has to rise farther before it saturates with enough water to form the cloud base.

CNN: Clouds' role in global warming studied

Funnel clouds look like cone-shaped or thin rope-like protuberances which hang down from the cloud base, and often do not last very long.

BBC: Funnel clouds, twisters, tornados: What are they?

Colin Le Ray said the system allowed planes to land in lower visibility by giving guidance to pilots, particularly when the cloud base was low.

BBC: Fog 'causes disruption' at Guernsey Airport