Why is it that the bottom base of clouds appear level and horizontal, never tilted up or down and never bumpy like the tops of the clouds are?
—Kathy B., Elgin
You are referring to cumulus clouds which has to do with the way in which cumulus clouds form. These clouds form when air rises and cools to its condensation temp, then begins to condense into white, cottony clouds that we see dotting the sky. At a given location, condensation occurs at about the same height above the ground (regardless of the terrain), and so the bases of the cumulus clouds are all located at about the same height. The tops of cumulus clouds have no such limitations, and are free to grow “as they see fit.” The result is a sky checkered with cumulus clouds, all appearing to start at about the same height above the ground, and then building upward from there.