Supercell
A supercell is a cloud formation that indicates severe weather is on the way. Supercells are associated with thunderstorms, hail, and even tornadoes. These tall clouds form when warm air rising from Earth's surface quickly reaches higher levels of the atmosphere and is therefore very unstable. As more and more air rises, the top of the cloud spreads out, forming an anvil shape or overhang. While precipitation (such as rain or hail) falls from one part of the cloud, another part of the cloud continues to draw in air. Under this updraft, tornadoes can form. Supercells don't guarantee tornadoes, but they do mean that some sort of severe weather is very likely to occur.