These are bands of cumulus clouds that extend out from the main thunderstorms. Typically, this is to the southeast or south. Inflow bands usually indicate that the storm is gathering low level air from around the storm. If there is a twist in the motion of the air, rotation is possible.
The beaver's tail
This is a smooth, flat cloud band extending from the eastern edge of the dry part of the cloud to the east or northeast. It usually skirts around the southern edge of the precipitation area. It also suggests the presence of rotation.
A wall cloud
The wall cloud is usually to the rear of the visible precipitation area. This may exist in the 10 to 20 minutes before a tornado appears. You may see rotation with it as well and even see debris going into it, as strong surface winds flow into it.
As the storm intensifies, the updraft draws in low-level air from several miles around. Some low-level air is pulled into the updraft from the rain area. This rain-cooled air is very humid; the moisture in the rain-cooled air quickly condenses below the rain-free base to form the wall cloud.
The rear flank downdraft (RFD)
The RFD is a downward rush of air on the back side of the storm. This will follow the tornado. The RFD looks like a slot just to the rear (southwest) of the wall cloud. It can also look like curtains of rain wrapping around the cloud base circulation. The RFD causes gusty surface winds that occasionally have embedded downbursts. The rear flank downdraft is the motion in the storm that causes the hook echo feature on radar.
A condensation funnel
A condensation funnel are fully of water droplets that extend downward from the base of the clouds of a thunderstorm. This is the image we most typically think of with a tornado, which is actually dust and debris. However, a condensation funnel does not necessarily mean a tornado. It will only be a tornado if it comes in contact with the ground. Otherwise, it is a funnel clouds.
Part of this article is borrowed from the National Weather Service.