| Low-Level
Features Some of the most critical cloud features for assessing thunderstorm severity and tornado potential are found at or below the level of the cloud base. While there is a lot of information to be discerned in these low-level cloud features, most of the confusion (and frustration) associated with storm spotting stems from attempting to interpret these similar appearing but meteorologically distinct cloud formations. Perhaps the easiest low-level feature to identify is the rain-free base (figure 19). As its name suggests, this is an area of smooth, flat cloud base beneath the main storm tower from which little or no precipitation is falling. The rain-free base is usually just to the rear (generally south or southwest) of the precipitation area. The rain-free base marks the main area of inflow where warm, moist air at low levels enters the storm. Some have called the rain-free base the "intake area" of the storm. We earlier discussed the domination by a storm of its local environment. Besides suppressing any nearby storms or clouds, this local domination can also show itself through the presence of inflow bands, ragged bands of low cumulus clouds which extend from the main storm tower to the southeast or south. The presence of inflow bands suggests that the storm is gathering low-level air from several miles away. The inflow bands may also have a spiraling nature to them, suggesting the presence of a mesocyclone. The beaver's tail is another significant type of cloud band. The beaver's tail is a smooth, flat cloud band which extends from the eastern edge of the rain-free base to the east or northeast as shown in figure 20. It usually skirts around the southern edge of the precipitation area. The beaver's tail is usually seen with high-precipitation supercells (which will be discussed later) and suggests that rotation exists within the storm. Lowerings of the rain-free base and "accessory clouds," such as shelf clouds and roll clouds, mark important areas of the storm. The next chapter will discuss wall clouds and other lowerings in more detail.
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