Herb Weiner . All rights reserved. Air currents do not cause water to rise in the air, as Marilyn claims.
Humid air rises because it is lighter than dry air, and is the cause of the updrafts.
As the humid air rises, it cools, causing water droplets to condense. At this point, Marilyn is correct in explaining that the updrafts sustain the clouds, since the water droplets are heavier than air. When the droplets grow large enough to overcome the updrafts, they fall as precipitation. Humidity and high temperature are the two causes of low pressure systems, since they both lower the density of air. High pressure systems, which are generally clear and free from bad weather, are caused by dry or cold air.