Definition:A shelf cloud is a low, horizontal, wedge-shaped arcus cloud which is attached to the base of the parent cloud, which is usually a thunderstorm, but could form on any type of convective clouds.
It is also called as arcus or arc cloud.
Rising cloud motion often can be seen in the leading or outer part of the shelf cloud, while the underside often appears turbulent and wind-torn.
People seeing a shelf cloud may believe they have seen a wall cloud since an approaching shelf cloud appears to form a wall made of cloud.
A shelf cloud usually appears on the leading edge of a storm.A 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.
A very low shelf cloud accompanied by these signs is the best indicator that a potentially violent wind squall is approaching.
Definition:Scud clouds are a type of fractus cloud which are low, detached, irregular clouds found beneath nimbostratus or cumulonimbus clouds.
They are often ragged or wispy in appearance. When caught in the outflow beneath a thunderstorm, scud clouds will often move faster than the storm clouds themselves.
Scud clouds are very commonly found on the leading edge of a storm front. In this area of a storm, scud are commonly associated with shelf clouds.
Scud clouds can often be mistaken for a developing tornado, landspout, or waterspout. The difference is determinable by identifying if there's any rotation (not just movement) of the scud clouds.
If any rotation occurs, a tornado, landspout, or waterspout has a high chance of forming.
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