Clouds can also form during the start of an eclipse, especially near a coastline or ridgeline where humidity is near dewpoint before temperatures fall. This de

Clouds can also form during the start of an eclipse, especially near a coastline or ridgeline where humidity is near dewpoint before temperatures fall. This describes how thermally driven cumulus clouds disappear. However, I'd also say that another big effect is that the sun simply isn't there to illuminate the light cloud layer. See Mauna Kea 1991: https://www.youtube.com/watch?v=_RIMjx8feew https://www.youtube.com/watch?v=_RIMjx8feew