ES1803  Observe clouds form and dissipate.
  !   Click the image to see the animation.

A steady supply of rising moist air is required to build cumulus clouds. As moist air rises to the condensation level, clouds begin to form. If drier air reaches the same level, clouds that had just formed can evaporate and disappear from view. Varying amounts of moisture in rising air result in clouds forming, then dissipating, in this time-lapse sequence.