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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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Created :
2002-08-26
Modified :
2002-12-19
Reviewed :
2002-12-19
Url of this page : http://www.msc.ec.gc.ca /education/severe_weather/page44_e.cfm
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