Severe Weather Watcher Handbook

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Rain shafts and virga

Another common deception is provided by distant shafts of falling precipitation, especially when silhouetted. Virga, or precipitation which evaporates before reaching the ground, often looks like dark,tapered extensions below a cloud base and, thus, like a funnel cloud.

A quick look around the sky will show the absence of an organized storm or lowering and closer inspection of these tufts will show they are diffuse and soft-edged. Individual rain shafts can be very deceiving. A thin, newly formed rain shaft under a distant cloud base can look just like a tornado. Time is on your side, though, because the scene will change rapidly and disqualify itself as the rain shaft widens or thins out again. The situation and location will be wrong as well. A particular problem can arise if such a rain shaft forms right behind a true wall cloud (making it look like it . s below,due to perspective). After a moment, the shifting perspective or expanding shower will eliminate an incorrect interpretation.

Roll clouds

A smooth cloud tube under a storm can look threatening because it resembles a horizontal tornado with its tapered, cigar shape. But these clouds are formed by gently-rolling outflow and only indicate forward-moving cool air. They are not attached to a solid, dark base and do not present any danger.

False rotation

A turbulent, stormy sky is full of different air motions and some of them will swirl in a circular pattern without being true, tornadic rotation. Sometimes the swirl is apparent from bits of scud moving around; at other times, the cloud base will have a circular spot or hole present. These are quite common under the shelf cloud when descending air currents rotate slightly (often counterclockwise). They can also be seen near or under the updraft region, but will be isolated and not accompanied by any lowering, funnel, or other expected signs.

False assumptions about tornadoes

A tornado's location and characteristics can be so unexpected that you may be easily fooled by your senses.

Unless you are paying close attention to storm structure, the calm under the updraft/lowering area can be very deceiving. Winds abate, precipitation ceases, and the stillness invokes subtle apathy. Only the abnormal darkness, often absent in the West, arouses your suspicions.

What you don't see can be devastating! Many tornadoes - including dry, high-based ones and low, wide ones - do not possess a typical condensation funnel that can be seen and recognized beforehand. There are signs of rotation, circular structure, etc. to rely on, but the actual ground contact may begin as a surprise to the observer.

The tornado's location on the southwest end of a severe storm should also be remembered. Many of the other storm characteristics will already have passed by and the sky may already be brightening. Countless tornado reports emphasize this apparent contradiction - of a violent visitor arriving just when things appeared to be improving!

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