'Thick Cloud' in the Bible

Yahweh said to Moses, "Behold, I come to you in a thick cloud, that the people may hear when I speak with you, and may also believe you forever." Moses told the words of the people to Yahweh.

It happened on the third day, when it was morning, that there were thunders and lightnings, and a thick cloud on the mountain, and the sound of an exceedingly loud trumpet; and all the people who were in the camp trembled.