Recognizing severe storm cloud features – storm spotting

 

During the transition to spring and summer in Lubbock, stormy skies become an all-too familiar sight, (thunder sound in background) bringing with them the potential for strong winds, heavy rains, hail, and even occasional tornadoes. But while it may seem that all of these thunderstorms bring with them the same hazards, they can actually be quite different from each other and in severity and type of severe weather they produce. Certain features in the cloud structures can reveal the hazards that each pose, and can help storm spotters and civilians alike to discern whether a given storm might be severe enough to pose a risk to life and property.

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A telltale sign of a typical well-developed storm is what is called a rain-free base. This is the region where a warm inflow of air is fed into the storm, suspending rain and hail and feeding the updraft for further development. The rain-free base appears as a dark cloud base with a lighter area underneath, and it often exhibits broad rotation. In some cases, a rotating lowering develops from this cloud base.

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An abrupt, persistent lowering from the base of a thunderstorm is called a wall cloud. Wall clouds are usually rotating, and are indicative of strong rising motion. It is important to watch wall clouds and note whether or not rotation is present, and how violent and persistent this rotation appears. When the rotation in these regions begins to intensify, it means a tornado may be imminent. Picture an ice skater spinning around in a circle; when she brings her arms in closer to her, she begins to spin faster. The same principle applies to tornadoes, which will produce destructive winds near the ground.

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Visually, this tightening rotation may first only appear as a funnel cloud, which indicates a strong vortex has formed.  Often, debris is present on the ground beneath the funnel, indicating that damage is already occurring at the surface.  That is, tornadoes do not need the condensation funnel to reach the ground.  In fact, Doppler-radar measurements suggest that many funnel clouds protruding from beneath a wall cloud are in fact tornadoes.  So, never drive underneath a funnel cloud!

Many severe storms will also produce hail, especially in West Texas. Falling hail is often visible on the western side of the storm and it will appear more white and wispy than surrounding rain. Another phenomenon is scud clouds, which are tricky in that are often mistaken for a tornado or funnel cloud. They are actually just small cloud fragments, often ragged in appearance, and they pose no danger. In order to discern scud from other, more serious cloud formations, be sure to look for rotation and a distinct connection to the thunderstorm base; if neither characteristic is present, those low clouds might just be scud.

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Storm spotting provides important and timely information to those in the National Weather Service, and as such, trained storm spotters are key to providing the most accurate and helpful information to protect the lives and property when the weather turns wild over West Texas.