Identifying wall clouds

[dmckemy]

Recently while chasing in North Carolina, I have come across several storms that have lowering bases that appear to be wall clouds. Most of the "wall clouds" are usually in the southern part of the storm, and I believe that they are wall clouds because usually I can see the upward motion of the clouds with it (indicating an updraft), and it's in the rain-free base of the cloud. Now, most of what I have seen in the past couple of weeks have been single/multi cell storms, so obviously these wall clouds have little, if any, rotation to them at all.

My question is, are wall clouds common in thunderstorms, and if so, how do you make sure that it's not scud you're looking at? What defines a wall cloud in non-supercell storms?

One example of what I'm talking about is below...this was taken today for a severe storm near Gastonia/Charlotte. The rain base/shaft is off to the left, a tail cloud (I believe) started to form off of what I think is a wall cloud.

 

[Skip Talbot]

I would say that well defined wall clouds are not common in thunderstorms. Your picture does look like a wall cloud, especially given the description you gave for your position relative to the storm. An easy way to tell a shelf cloud from a wall cloud is the way it points. If it points towards the rain its typically a wall cloud, if it points away its typically a shelf cloud. Here you described the rain as off to the left and indeed that does look like a tail cloud on the left. As for scud. Observe the storm. Is the scud rising into the storm in an area of inflow? Do you feel winds going into the storm? Scud may build to form a wall cloud so we typically look for it to assume some recognizable structure and for it to have some staying power of at least a few minutes and for it to remain in the same place relative to the storm. If its just scud its probably going to fade away within a minute or move off of the area you suspect to be a wall cloud.

 

[Tim Shriver]

While they may not be overly common, I do think they occur more
then many think.

Rotating wall clouds are much more uncommon.

But if the storm has some good inflow/updaft to it, it may form
one as it is only a collection of moisture from the air being pulled in.

Tim

 

[Phil Kurimski]

In addition to Skip's point of which way the cloud is pointing the winds and movement are also a good indicator of what cloud you are looking at.

A wall cloud will typically not move much and you will have the wind blowing towards the wall cloud.

A shelf cloud on the other hand will tend to move with winds shifting and blowing in your face as the feature gets closer to you.

The complicating factor is scud...which could occur with either wind direction. The main thing to look for with scud is these clouds will tend to change shape very quickly...while wall and shelf clouds will generally maintain themselves for several minutes. Even though they may change shape they do so much slower than a transient scud cloud will.

 

[dmckemy]

Thanks for all the help/comments so far! I have one other question...do wall clouds in non-supercell storms form in the southwest side of the storm, or can it vary? Most of the ones that I have encountered so far seem to form there, but I was wondering if the wall cloud formation position was similar to supercells.

Also, I had another question about another photo...this was a photo of a non-supercell thunderstorm that I took on June 11th. At this point, I was on the south side of the storm facing north, and I believe that the lowering in the picture is a wall cloud (the rain base/shaft is off to the right). Thoughts?

 

[Tim Balassie]

dmckemy -

Trying to identify certain types of cloud features from photos can be a tricky proposition. The principle reason is that the life-cycle of a Cb is the life-cycle of a process. A photo captures this process in one instant of time. To assess what is occurring during the course of the process you have to take the time to observe it in action (this is a generality; I'm not citing you personally as an example).

Both photos may be wall clouds, or they may be areas where some type of inflow-outflow interface is occurring (which is where I'm leaning, but ...). The fact that you're observing these features from the SW may or may not be relevant. It depends on from where the Cb is ingesting inflow. Idealized views of supercell life-cycle have the SW quadrant of a NE moving Cb the main area of inflow. But I think as many on this list will tell you there are differences between reality and the "textbook" view. Storms do funny things, which is why they're so interesting to watch.

Concerning wall clouds, I think Skip Talbot's and Tim Shriver's opinions are equally valid and not incompatible. There are a myriad of factors in play, such as updraft strength, the thermodynamics of the inflow layer, etc. I do believe, after looking at many pictures and videos over the years that "wall cloud" might be slightly over-ID'd.

Not sure this added anything to the discussion ...

Tim Balassie (KC9JIB)
Kane Co, IL

 

[dmckemy]

Tim-

Thanks for the input! I guess my mindset with wall cloud positions was with "textbook" examples and expecting them to be in the SW side...but what you said makes sense.

I guess my main problem was determining at what point scud can "become" a wall cloud (if there is scud), but I think I have a better grasp on it now. By the way, if anyone knows of any articles/journals/anything that goes into detail about wall clouds for supercelluar and non-supercelluar storms, please let me know. Thanks, and I appreciate everyone's help!