arcus (arc)

A low, compact cloud, shaped like a horizontal arch or roll, that appears at the leading edge of some storms, attached to the base of the corresponding cumulonimbus. Dark and threatening, in its lower part the strong prevailing wind gusts (gust front) literally tear the cloud apart, forming ragged shreds that give that lower part a frayed appearance. Its Latin name is the one established by the WMO International Cloud Atlas for the supplementary feature described.