This is a quote from a report this past weekend by
On the morning of the 16th April 2009 a sharp trough situated to the North West of Cape Town was resulting in some unstable weather with a risk of thundershowers in the area. At 08:15 it was noted on the Cape Town Webcam that a small amount of mammatus were evident near Table Mountain, during the next 15 minutes the mammatus clouds started developing rapidly along the edge of the passing cloud band. Mammatus usually form on the dying anvils of cumulonimbus clouds on very rare occasions; but some times they form at the bottom of dense altocumulus clouds as was the case on the 16th. By 08:30 there was a widespread mammatus event which spanned tens of kilometers and was heading from the north west to the south east. At 08:45 these mammatus had passed Somerset West and was heading towards Grabouw area, while they had lost some of their structure they continued developing as the clouds stretched further south east. The longivity of these mammatus were also unusual as mammatus tend to have a life-span of just a few minutes and even at 09:00 they were evident in the distance over the hottentots holland mountains.
Credits to www.capetown-webcam.com for the above image.
On the morning of the 17th the sharp trough had developed into a weak cut-off low and there were numerous cumulonimbus clouds accompanied by some thunder and lightning as well as fairly light rain. While there were no other reports of mammatus on this day I managed to catch a dying cumulonimbus cloud drop a small area of mammatus.
A very exciting event for all those who saw the spectacle, many people will only live to see an event like that once in their life and the general public seemed to notice the clouds too as they made the front page of numerous newspapers and was the topic of conversation for the next few days. It was a very humbling experience, words and photographs can not really descripe how amazing it is to be confronted by these clouds.