Roll Cloud at South Oliphant, Ontario - 5/27/2007

South Oliphant, Ontario - 5/27/2007

  This weather phenomenon, known as a "Roll Cloud", stretched across the sky and spun in a spiral rotation on May 27, 2007.
  The cloud came in off of Lake Huron and passed over Chief's Point and the family's property at the southern end of Oliphant in Bruce County, Ontario. They quickly realized that this cloud was being pushed by a cold air mass as the temperature dropped from the low-70s down to the mid-50s in about 3 minutes. Chilly gusts of wind picked up as the cloud passed overhead.

Roll cloud

A roll cloud in Uruguay.

A roll cloud is a low, horizontal, tube-shaped, and relatively rare type of arcus cloud. They differ from shelf clouds by being completely detached from other cloud features. Roll clouds usually appear to be "rolling" about a horizontal axis. They can be described as a solitary wave or a soliton, which is a wave that has a single crest and moves without changing speed or shape. One of the most famous frequent occurrences is the Morning Glory cloud in Queensland, Australia. One of the main causes of the Morning Glory cloud is the mesoscale circulations associated with sea breezes that develop over the Cape York peninsula and the Gulf of Carpentaria. However similar features can be created by downdrafts from thunderstorms and are not exclusively associated with coastal regions.
Coastal roll clouds have been seen over California, the English Channel, Shetland Islands, Lithuania, Eastern Russia, other maritime regions of Australia, off the Mexican coast in the Sea of Cortez, Uruguay, in the Canadian provinces of Nova Scotia and Ontario and Campos dos Goytacazes and Coronel Vivida bay in Brazil.