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The gust front ushers in a cool gusty wind, either just ahead of the heavier
precipitation or along the flanking line. Too much outflow can push the gust
front far ahead of the storm, eventually cutting off the inflow. The storm will
then stop regenerating and weaken. A detached gust front/shelf cloud may become
a roll cloud (a long horizontal tube) before evaporating, or may rebuild
new cumulus towers that will spawn a new storm later. But if the flanking line
remains intact and connected to the original storm, inflow will continue and
the storm can revive and reassert its former strength and structure.
Types of storms
There are three simplified storm types:the single cell; the multicell, and
the supercell. Each has a distinct structure, circulation pattern, and set of
updraft/regeneration charateristics. Thinking about their differences can help
you interpret the clouds you see.
A single-cell thunderstorm is one whose life cycle portrays the growth
and collapse of a single updraft cell. The cloud forms, grows to maturity, produces
a heavy downpour, and then decays as downdrafts suffocate and dilute the original
warm inflow. Such storms are common in mid-summer and usually last no
more than an hour. They are ordinary,harmless events that almost never produce
any severe weather.In rare cases,a strong single-cell storm called a pulse
storm can produce brief damaging winds during its collapse phase.
The multicell storm type is the most common and consists of successive,
separate updraft pulses which maintain a more or less steady state for the system's
overall strength, structure,and appearance. The pulses may be very close together
- causing the storm's characteristics to be quite uniform over time - or they
may be widely spaced, resulting in a storm that cycles repeatedly through stronger
and weaker phases.These pulses in the system can be seen from a distance by
watching the spacing and growth rate of individual cumulus towers along the
flanking line as they merge with the main storm cloud.Each one may be part of
a solid, continuous base but they mature as separate steps, adding their distinguishable
contribution to the storm - precipitation pattern and anvil structure. When
all factors are considered, the cloud system can be quite varied and provides
an excellent opportunity to observe the convective life-cycle in continuous
evolution. Multicell storms can cause all the severe effects, but they produce
infrequent and short-lived tornadoes.
9 A typical multicell storm with a succession of rising towers along
the flank (lower left). As each one matures, it spreads out to become the anvil
at the top and the current core with heavy rain below. The rain and cool downdrafts
then provide a "barrier" against which the warm air rises to form the next tower
down the line. If the updrafts are strong enough, there may be a lowering on
the inflow-outflow boundary under the storm.
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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/page07_e.cfm
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