Some general characteristics help identify supercells from a distance.
Air rising into the storms at speeds up to 170 mph helps give them a hard, cauliflower look. The air is turning as it rises, which can give parts of the clouds a corkscrew appearance. Tornadoes, especially large ones, usually drop from the supercell near the edge of the rain-free area under the storm. The millions of tiny water droplets and ice crystals that we see as a cloud hides much of the action going on inside a supercell thunderstorm. But, the appearance of the cloud helps show what's happening inside.