In this stunning capture by Gonzalo G. Useta, we see a massive shelf cloud off the coast of Montevideo, Uruguay. A shelf cloud is a low, horizontal, wedge-shaped Arcus cloud. They are typically attached to the base of a parent cloud, which is usually a thunderstorm, but could form on any type of convective cloud. [Source]

Rising cloud motion often can be seen in the leading (outer) part of the shelf cloud, while the underside often appears turbulent and wind-torn. Cool, sinking air from a storm cloud’s downdraft spreads out across the land surface, with the leading edge called a gust front. This outflow cuts under warm air being drawn into the storm’s updraft. As the lower cooler air lifts the warm moist air, its water condenses, creating a cloud which often rolls with the different winds above and below (wind shear). [Source]

Montevideo is the largest city, capital and primary port of Uruguay. Established in 1724 by the Spanish soldier Bruno Mauricio de Zabala, Montevideo has a population of 1,319,108 as of 2011 (about one-third of Uruguay’s population). [Source]