Clouds

The clouds we see are only the visible portion of much larger convection currents. It is like seeing a person's smiling head on the beach. You know there is a body under the sand. With clouds, the part we see is the part that has cooled to below the dew point. The cooling comes when the air rises to a higher altitude, at a lower pressure. The flat bottom to most clouds is that altitude where pressure is reduced, therefore temperature is reduced to the dew point. If the air is below the dew point all the way to the ground, we have fog.