Tornadoes can also occur in other severe thunderstorms known as multicells. Severe multicells differ in their structure from supercells in that they are normally not associated with a rotating structure. Multicell structure involves the development of newer adjacent cells as other cells die. Tornadoes that occur will normally develop in the mature or developing cells. Although the dynamics of tornadic development are very complex, the visible features of tornadoes are generally similar.
MOST tornadoes develop from lowered rotating bases known as wall clouds.
These wall clouds are normally located at the northwestern section of thunderstorms in the southern hemisphere and in the southwestern region of thunderstorms in the northern hemisphere. This region of the thunderstorm is known as the flanking line which consist of a line of large cumulus decreasing in size outward from the rear of the storm. Even though most tornadoes descend from wall clouds, there are occasions where tornadoes descend straight from the thunderstorm itself with no wall cloud. The wall cloud region is usually a region with little or no precipitation. As a supercell passes over, an observer notices an extensive anvil becoming thicker and gradually darker.