It's great to see the differential lighting effects created by a sun lowering towards the horizon on clouds with a large vertical component.
A cumulonimbus is quite a regular site on the high-veld in the late afternoon and I shot this one while waiting for my evening train commute home.
What is awesome about these cells is the high level of complex inflows, outflows, up and down drafts etc. This is well illistrated in this pic below.
A simplified side-on view shows the clear flat top that usually forms on these storm cells, its also great to be able to see when looking at these cells, at a glance, the interface between the tropopause and the troposphere.
The portion of these storm cells that never ceases to amaze me in its variety and uniqueness. The mammatus clouds which hang down from the spreading flanks.
They always produce great visual effects when lit from underneath by a setting sun as can be seen in these couple of images found with a basic google image search on "mammatus clouds"
