A WALL CLOUD is the lowering of a portion of the cloud base beneath a thunderstorm. A wall cloud forms in the rain-free base of a thunderstorm and is located where the updraft and the downdraft interact.

Other cloud formations, like scud clouds, can mimic a wall cloud in appearance. If these clouds are not attached to the thunderstorm base or fade away fast, they are not wall clouds. A wall cloud is ATTACHED to the rain-free base of a thunderstorm cloud. Wall clouds exhibit rapid ROTATION and vertical, upward motions.

In wall cloud identification, the important thing to look for is ROTATION.

Is the lowered cloud rotating in a CIRCULAR MOTION? If the answer is yes, you are most likely looking at a wall cloud.

If DIFFERENT CLOUDS are moving in DIFFERENT DIRECTIONS, you are most likely seeing what is known as "SHEAR."

These clouds are not wall clouds. Shear is very common in all thunderstorms.

All storm spotters need to know the difference between random horizontal cloud motion, or SHEAR and actual wall cloud ROTATION.

When you are storm spotting, take several minutes to look at the clouds and determine if there is rotation. Pick a few distinctive cloud elements and watch long enough to assess if the motion is circular. Do the cloud elements revolve around a central point? If so, you are likely observing rotation. If clouds are seen moving in two different directions but no circular motion is observed, it is just shear.

In addition, once a wall cloud is developed, it will maintain its location relative to the updraft/downdraft interface (as it is dependent on them). Storm Chasers also report that wall clouds that produce tornadoes, persist for "tens of minutes" before a tornado forms.

Often times a wall cloud will develop a sloped or "pointed" end. Usually this end points toward the downdraft or area of rainfall. This is know as a TAIL CLOUD. Here we see a wall cloud with an attached tail cloud pointing toward the heavy rain area.

IN SUMMARY: Wall clouds are attached to the bases of thunderstorm in the rainfree areas. Tornadic wall clouds are persistent over tens of minutes, have surface-based inflow, and exhibit rapid rotational and vertical motions.