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Shelf cloud in portuguese12/23/2023 Roll clouds usually appear to be "rolling" about a horizontal axis. They differ from shelf clouds by being completely detached from other cloud features. Source: Wikicommons Roll CloudĪ roll cloud (Cloud Atlas name volutus) is a low, horizontal, tube-shaped, and relatively rare type of arcus cloud. Shelf cloud seen over Enschede, The Netherlands, July 2004. An extreme example of this phenomenon looks almost like a tornado and is known as a gustnado, a small, usually weak vortex. A very low shelf cloud accompanied by these signs is the best indicator that a potentially violent wind squall is approaching. In a severe case there will be vortices along the edge, with twisting masses of scud that may reach to the ground or be accompanied by rising dust. This is a mistake, because although an approaching shelf cloud appears to form a wall made of cloud, shelf clouds usually appear on the leading edge of a storm, while wall clouds are usually at the rear of the storm.Ī sharp, strong gust front will cause the lowest part of the leading edge of a shelf cloud to be ragged and lined with rising fractus clouds. People seeing a shelf cloud may believe they have seen a wall cloud often associated with severe weather. As the lower and cooler air lifts the warm moist air, its water condenses, creating a cloud which often rolls with the different winds above and below (wind shear). This outflow cuts under warm, stable air being drawn into the storm's updraft. Cool, sinking air from a convective cloud's downdraft spreads out across the land surface, with the leading edge called a gust front. Rising cloud motion can often be seen in the leading (outer) part of the shelf cloud, while the underside often appears turbulent and wind-torn. A shelf cloud is attached to the base of the parent cloud, which is usually a thunderstorm cumulonimbus, but could form on any type of convective cumulus clouds. Shelf CloudĪ shelf cloud is a low, horizontal, wedge-shaped arcus cloud. Roll clouds may also arise in the absence of thunderstorms, forming along the shallow cold air currents of some sea breeze boundaries and cold fronts. They most frequently form along the leading edge or gust fronts of thunderstorms. Roll clouds and shelf clouds are the two main types of arcus clouds. Technicall an "accessory cloud" which is in association with other cloud types, it occurs with Cumulonimbus (Cb) and, less often, with Cumulus. A dense, horizontal roll with more or less tattered edges, situated on the lower front part of certain primary clouds and having, when extensive, the appearance of a dark, menacing arch. (English) Meteorological Service of Canada (Decembre 19th, 2002).Wikimedia Commons has media related to: Arcus Wikimedia Commons has media related to: Shelf cloud Wikimedia Commons has media related to: Roll cloud Morning Glory cloud - an extremely long and even more rare variety of roll cloud.An extreme example of this phenomenon looks almost like a tornado and is known as a gustnado. In a severe case there will be vortices along the edge with twisting masses of scud that may reach to the ground or be accompanied by rising dust. Sign of dangerĪ sharp, strong gust front will cause the lowest part of the leading edge of an arcus to be ragged and lined with rising fractus clouds. Generally speaking, a shelf cloud appears on the leading edge of a storm, and a wall cloud will usually be at the rear of the storm. This is a common mistake, since an approaching shelf cloud appears to form a wall made of cloud. Occasionally people seeing a shelf cloud may believe they have seen a wall cloud. Rising cloud motion often can be seen in the leading (outer) part of the shelf cloud, while the underside often appears turbulent and wind-torn. Unlike a roll cloud, a shelf cloud is attached to the base of the parent cloud (usually a thunderstorm). A shelf cloud over Enschede, Netherlands.Ī shelf cloud is a low, horizontal wedge-shaped arcus cloud.
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