Wall cloud or scud?

While driving back to work from a lunch break at home one afternoon on the 30 October 2012, I noticed this rather unusual feature in the distance during a storm that was hovering over the Waterkloof Air Force base in Centurion. Being the curious weather observer that I am, I immediately pulled over to the side of the road to observe the storm in more detail and of course took out my camera to take pictures.

 

The feature that caught my attention in the centre of the picture. Was it a wall cloud, or was it just scud clouds?

 Looking at it, and having seen pictures in books and storms in documentaries on tv, I immediately got very excited at the possibility that I may be witnessing the formation of a wall cloud. I was a little anxious too as it was hovering over a densely populated area and should anything have happened, it would have been potentially devastating indeed.

I stood by the side of the road for about 20 minutes watching it as it hovered almost in one place maintaining that form almost the entire time I was watching it. Unfortunately I believe due to the distance it was from me, I couldn't tell whether it was rotating or not and admittedly even from that distance I could see that it didn't seem to have a very solid structure, as wall clouds usually do. My confusion was further exasperated when I posted the pictures on several weather sites hoping to get some insight into what this feature was. Some agreed that it was indeed a wall cloud, while others dismissed it as just scud clouds that just happen to look like a wall cloud. 

The feature looking even less organised as it continues to hover over Waterkloof Air Force Base.

 The word scud is actually an acronym for "scattered cumulus under deck" and refers to low hanging, detached clouds that are usually found in the outflow of a thunderstorm. They're usually very fast moving and irregular in their movements. Because they swirl and move about the base of thunderstorms, scud clouds are very often mistaken for wall clouds and sometimes even funnels and tornadoes. So how do you spot the difference between a scud cloud and a tornado or wall cloud. http://en.wikipedia.org/wiki/Scud_%28cloud%29.  

Normally one way to tell if you're looking at scud clouds or wall clouds or tornadoes is to look for any visible signs of rotation. Because scud clouds are detached from the thunderstorm base, they do not rotate and although their swirling motion may appear to be rotation, it is irregular and does not follow a constant pattern of movement in any one particular direction. 

Very tornado like scud clouds in Denver, Colorado in 1999. (Courtesy of Christine White)

 The photo above is a perfect example of why it is so easy to mistake scud clouds for tornadoes or wall clouds. As frightening and ominous as these clouds look, they were actually scud clouds that formed as a result of outflow from a gust front as it moved over Denver. There was no rotation or violent movement of any kind and no damage was reported in the area it moved over. For more information of this feature visit http://www.stormeyes.org/tornado/faq/notahose.htm.

Scud clouds that resemble a wall cloud below the the base of a thunderstorm (Courtesy of Jim South)

Tornado like scud in the American Midwest. (Courtesy of Bernard Hulshof)

I myself have been duped by Mother Nature on several occasions having witnessed swirling clouds that appeared very close to the ground and appeared to be in some way rotating and I've thought I might be witnessing the birth of a tornado. Only to find that it was nothing more than some harmless scud clouds. Although scud clouds themselves pose no threat to people or structures on the ground, they are however a sign that severe weather is on the way as they indicate the presence of low level moisture which is a key ingredient in the development of strong thunderstorms. http://valleywx.com/2012/07/27/scud-cloud-picture-from-woodville/

How it looked in the distance in relation to the rest of the storm