"A Roll Cloud Over Wisconsin" by Megan Hanrahan (Pierre cb) [1024x768] - link to [3072x2304] in post

Hi-res version (3,072 × 2,304)

Source: https://en.wikipedia.org/wiki/File:Roll-Cloud-Racine.jpg

Via APOD: 2023 August 20 – A Roll Cloud Over Wisconsin

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 cloudsmay 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. http://commons.wikimedia.org/wiki/File:Roll-Cloud-Racine.jpg, a roll cloud extends far into the distance as a storm approaches in 2007 in Racine, Wisconsin, USA.