Cumulus castellanus cloud

Cumulus castellanus (from Latin castellanus, castle) is an unofficial name of a species of cumulus cloud that is distinctive because it displays multiple towers arising from its top, indicating significant vertical air movement. It is a misnomer for cumulus congestus and correspondingly can be an indicator of forthcoming showers and thunderstorms. The World Meteorological Organization and the American Meteorological Society do not recognize cumulus castellanus as a distinct species, but instead classify all towering cumulus clouds as Cumulus congestus.^[1]

Cumulus castellanus
Cumulus castellanus low on the horizon
Appearance	Flat on the bottom, though has multiple "towers" on top
Precipitation	Usually, but not always