
Image Credit: Megan Hanrahan (Pierre cb), Wikipedia Explanation: What kind of cloud is this? 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. A
roll cloud is not thought to be able to morph into a
tornado. Unlike a similar
shelf cloud, a roll cloud is completely detached from their parent
cumulonimbus cloud.
Pictured above, a
roll cloud extends far into the distance as a storm approached in 2007 in
Racine,
Wisconsin, USA.