When a humilis cloud grows vertically it turns into a congestus cloud. This happens normally later in the day when the heat-boosted vertical movements increase. The humilis clouds simply grow in size but are just as many. If you compare this picture with the humilis formation, you notice the difference in thickness.

Again, you notice the thickness and volume of these congestus clouds being greater than the humilis formation.

These two congestus formations are typical. The first one seen in a distance with its typical flat bottom. Too big to be a humilis but not yet giving any unstable surroundings like rain. The second formation is at the same place over the sea, but at sunrise.

The cloud-base is not always flat. This congestus is growing without retaining its typical flat bottom.

A beautiful congestus in the evening sun. Majestic!

Typical cumulus spreading somewhat to the sides when conditions are stable, that is in a high-pressure weather-area suppressing vertical movements.

These close-up pictures show only the top side of the clouds and are from fairly low altitude. The cloud base is flat, however, retained from its humilis stage. The two photos are from the same afternoon and location but in different lighting.

One might wonder where the change from congestus to calvus is. Well, this cloud formation could be either. Its cloud base is quite low but the top, seen here, reaches medium level altitudes.

This is not a typical example of a congestus cloud but looks more like a mystery cloud with its colours and strange form in the evening light. It's almost like an artist has been there with a paint brush.