Roll Cloud Over Wisconsin . ... A type of arcus cloud called a roll cloud . These rare long clouds may form near advancing cold fronts. In particular, a downdraft from an advancing storm front can cause moist warm air to rise , cool below its dew point , and so form a cloud . When this happens uniformly along an extended front, a roll cloud may form. Roll clouds may actually have air circulating along the long horizontal axis of the cloud. ... NASA Official: Jay Norris. ...