Severe Weather Watcher Handbook

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When appearances are deceiving

Our senses are very effective and the things we feel have a powerful influence on our thinking and assumptions. A severe storm is a very well organized structure with precise reasons for everything that happens or is seen by us. When you master its blueprint and behaviour you can prove or disprove every idea that occurs to you and anticipate its next move with enough certainty to become confident in our intuitions and assumptions.

Other surprises

Some of the darkest, most turbulent skies are harmless. The chaotic mix of dark and light blotches, with spiked, ragged edges and a strong breeze blowing outside are often seen with an outflow surge.

The normally smooth cloud base is punctured by numerous small downdrafts, giving the cloud an ominous appearance. Other than the wind, however, there is no danger whatsoever. Another example of this is mamma. These are rounded pouches or bulges protruding from a storm's anvil underside. They are dramatic, beautiful adornments, especially when sidelit. They have long been associated with severe weather, but their presence merely indicates descending pockets of small droplets or crystals from the anvil and poses no threat at all. The storm may be severe elsewhere but the mamma usually appear on the outflow side of the system under the anvil, away from the heavier precipitation.The rain core and its strong downdrafts cause a few peculiar lighting situations that can be deceiving. In the descending rain area, lower clouds are absent, causing this part of the sky to become relatively bright.

Such a bright glow sometimes follows the gust front but precedes a heavy downpour. Instead of clearing, the lighter sky heralds the worst weather of all! The sky can also display a greenish colour near the rain core or behind the gust front, but this is not related to tornadoes and represents no threat.

Dust plumes

One last reminder about dust or dirt rising from distant fields.Any strong wind gust will lift a cloud of dirt into the air and turbulent motions will mix it upward. If it is a microburst, the dirt will be concentrated, with a sharply defined forward edge and be angled forward. If it is a tornado debris cloud it will move more slowly, remain compact and symmetrical, and soon take the shape of a column. Without this discrete structure under the correct part of the storm, the event is more likely due to strong straight-line winds. The one exception is a dust devil, a column of whirling dust that looks like a mini-tornado but occurs exclusively on fair, dry days and is relatively harmless.

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