![]() On very rare occasions, one can view several roll clouds appearing in succession. What makes a roll cloud unique is that it appears as a solitary independent cloud, completely detached from any parent cloud. Although it is still viewed as a type of arcus cloud, the World Meteorological Organization (WMO) recently classified it as an entirely separate cloud species. In the WMO's Cloud Atlas, it is now officially called volutus clouds. The biggest reason for their scarcity is that the weather conditions have to be close to perfect for them to occur. It is no less spectacular than well-documented cloud systems but is a relatively rare occurrence. One needs to take a closer look to understand its unique characteristics, but one first needs to define it more clearly:Īs already stated, the appearance of roll clouds is a rare occurrence. It is the second of the two types of arcus clouds.Īlthough a roll cloud is classified as an arcus cloud, it differs significantly from its more famous cousin, the shelf cloud. Roll Cloud: Shelf Clouds' Less Famous CousinĪ lesser-known type of arcus formation is called a rolling cloud. As the warm air keeps rising along this border, it cools down, and condensation takes place, which results in the formation of a shelf cloud. It is along this boundary between the warm updrafts and cold downdrafts that shelf clouds form. From the fifth point, though, the process is unique to the development of shelf clouds:Īs the cold air from the outflow boundary (leading edge of the storm) moves forward, it tilts the rising warm air along its boundary. The formation of a shelf cloud is identical to the process described earlier in this post. These clouds don't appear that often but are almost as spectacular as the shelf cloud itself.) Shelf Cloud Formation (The dark, turbulent stretch between the edge of a shelf cloud and a thunderstorm is sometimes characterized by a distinct wavy appearance, known as asperitas clouds. This stretch of weather slots in between the appearance of shelf clouds and the arrival of the thunderstorm. Shelf clouds appear at the leading edge of this dangerous storm front, and although they pose no danger themselves, their appearance point to the looming threat of the derecho that follows close in its footsteps.Īs a shelf cloud passes overhead, it is usually followed by a dark tumultuous section of sky commonly known as the whale's mouth in meteorological circles. ![]() The familiar ragged-looking underside of a shelf cloud is a result of turbulent winds, as well as wind shear caused between the updrafts and downdrafts.Īrcus clouds in the shape of shelf clouds are synonymous with a derecho, a widespread and potentially devastating storm system you can read all about in this article. They are also often a precursor to cumulonimbus clouds. Congestus clouds are cumulus clouds that are taller than they are wide, in other words, with strong vertical development. Many wall clouds do rotate, however, some do not.Shelf clouds usually develop out of the parent cloud called a cumulus congestus cloud. Rotating wall clouds are an indication of a mesocyclone in a thunderstorm most strong tornadoes form from these. It is typically beneath the rain-free base portion of a thunderstorm and indicates the area of the strongest updraft within a storm. What is a Wall CloudĪ wall cloud is a large, localized, persistent, and often abrupt lowering of cloud that develops beneath the surrounding base of a cumulonimbus cloud and from which tornadoes sometimes form. It may appear to rotate on a horizontal axis. The wind will come first with rain following behind it. A shelf cloud will usually be associated with a solid line of storms. Oftentimes, these tornadoes are rain-wrapped and short-lived. Remember, that the main threat with any squall line is severe damaging winds associated with the shelf cloud, although brief spin-up tornadoes can occur. Below is a brief review of what a shelf cloud, wall cloud, and funnel cloud look like. Shelf clouds are often associated with squall lines, and many times they are reported as wall clouds, funnel clouds or rotation. ![]() In this article, we outline the difference between the two, as there is a major difference. However, some people miss label a shelf cloud as a wall cloud. The angry-looking sky causes people to take lots of pictures and send them our way, which we greatly appreciate, as long as you are doing it in a safe manner. Every spring, severe storms cause some really awesome or perhaps some scary-looking skies, depending on how you view it. ![]()
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