What forces drive the water vapor to form the shapes every child draws? Why isn't water vapor forming an uniform mist layer consistently (which it some times does)?

I have two general ideas how this process can self-sustain itself

• the shade of a forming cloud reduces sunlight to raising and condensing vapor
• the shade of the forming cloud causes varying speeds for vapor raising from the shade and from outside the shade on the ground, causing varying rate of condensation .

Neither of these, however, can tell me how the formation of a lump happened in the first place