Shelf vs. Wall Cloud

Tonight, we observed a pretty spectacular shelf cloud ahead of a line of severe thunderstorms. But shelf clouds are often mistaken for wall clouds, which produce tornadoes.

Let’s take a look at a case example. On the left, a wall cloud. On the right, a shelf cloud, taken by Vicki Lay in Davis Junction, Illinois tonight. At first glance, they look extremely similar. However, they are indicators of much different weather.

A wall cloud hangs lower than the base of the thunderstorm cloud. In this example, a tornado would form in the middle of the lowering part of the rotating wall cloud. Most of the time, you can observe the wall cloud actually spinning, albeit quite slowly to the naked eye.

A shelf cloud on the other hand (right) is a wide row of clouds arcing out ahead of a thunderstorm. In Vicki’s case, the storm is moving from right to left. A lot of times, there are low-hanging clouds under the base of the shelf. These are called scud clouds. A lot of times, scud clouds hanging from the bottom of a shelf are mistaken for funnel clouds. However, if you observe scud clouds, they may have upward movement but rarely spin.

Good rule of thumb is when you see a real funnel cloud, you’ll know it! You will definitely be able to observe the spin. And remember the old-fashioned stormchasing saying “If it doesn’t spin, don’t call it in!” -Eric


Posted under weather geek

This post was written by qni_it on May 30, 2013

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