While clouds over mountains are not unusual elsewhere, these clouds north of Los Angeles are. For the past few days, huge billows of clouds form during the late morning/early afternoon over these mountains, but do not spread into the L.A. basin. No one I’ver talked to remembers this happening before or has a clue why. The rest of the sky is nearly cloudless.

L.A. has been extremely hot and quite humid lately. The area behind the mountains is desert. Anyone know why the clouds are there?


Update: In the comments, Sandi notes these clouds are formed by orographic lifting 

When air is confronted by a mountain, it is lifted up and over the mountain, cooling as it rises. If the air cools to its saturation point, the water vapor condenses and a cloud forms.

These types of clouds are called “orographic clouds”, which develop in response to lifting forced by the topography the earth.