Weather 101: Shelf cloud vs. Wall cloud

With the Friday night storms that moved through the Twin Cities area, there were many calls from the public into “The Good Neighbor” and folks on Twitter reported seeing a wall cloud close to their location. Was it actually a wall cloud? No. What these people were actually seeing was a shelf cloud with the line of storms. A couple friends pointed out to me when I arrived home from following the storms that even television media outlets were not immune from making this error while posting images.

I felt compelled to write this post to help educate what is being seen in the sky to avoid confusion in the future. At the end of the day, does all of this make a huge difference? No, but I think accuracy counts, and it makes it easier to listen to reports on the radio when they are 95% correct rather than 95% wrong. What I’m not going to do is “call out”, because quite frankly, a lot of people out there simply don’t know the difference, and it would be arrogant of me to do so otherwise. One of my goals as being a storm spotter is connecting with the public and educating people that see my work through my blog or social media websites, so they have a better understanding and appreciation for weather. I try to present weather as a fun, interesting, and informative topic. It can actually be pretty cool!

So without further ado, here is the difference between the two cloud formations:

Shelf cloud at the National Weather Service in Chanhassen

The shelf cloud is horizontally elongated, and it’s something you typically see with a line of storms rather than an individual supercell thunderstorm. Winds are blowing away from a shelf cloud – known as the outflow. The National Weather Service defines it as, “A shelf cloud is a low, horizontal wedge-shaped cloud, associated with a thunderstorm gust front (or occasionally with a cold front, even in the absence of thunderstorms). A rising cloud motion often can be seen in the leading part of the shelf cloud, while the underside often appears turbulent, boiling, and wind-torn.”

Wall cloud image from the National Weather Service

Whereas the shelf cloud has more of a horizontal feature to it, a wall cloud on the other hand is a vertical lowering of the cloud base. These are what you see with rotating supercell thunderstorms, and are often a pre-cursor to funnel clouds and tornadoes if the conditions are just right. Winds are blowing towards a wall cloud – known as the inflow. The National Weather Service defines it as, “A wall cloud is a cloud formation associated with thunderstorms. It is a definite lowering of the cloud base typically beneath the rain-free portion of a cumulonimbus cloud, and indicates the area of primary and strongest updraft which condenses into cloud at altitudes lower than that of the ambient cloud base. Sometimes, the wall cloud will often be seen to be rotating. A rotating wall cloud is the area of the thunderstorm which is most likely to produce tornadoes, and the vast majority of intense tornadoes.”

Hope you found this to be informative for when you see weather roll in next time, you will know exactly what you are looking at!

RS