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Chapter 10: Thunderstorms and Tornadoes
The Atmosphere:
An Introduction to
Meteorology, 12th
Lutgens • Tarbuck
Lectures by:
Heather Gallacher,
Cleveland State University
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Copyright © 2013 Pearson Education, Inc.
What’s in a Name?
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Cyclone refers to the circulation around a
low-pressure center.
 Hurricanes
 Midlatitude cyclones
 Tornadoes
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Thunderstorms
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Thunderstorms generate lightning, thunder, winds,
and hail.
There are two types of thunderstorms.
 Air-mass thunderstorms are associated with warm, humid
air that rises in unstable environments; cumulonimbus
clouds, and mT air masses.
 Severe thunderstorms may produce high winds, hail, flash
floods, and tornadoes.
 They are the result of uneven heating, frontal lifting, and
diverging winds.
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Air-Mass Thunderstorms
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Air-mass thunderstorms—mT air masses
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Air-Mass Thunderstorms
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Stages of development:
 Cumulus
 Mature
 Dissipating
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Cumulus stage:
 A cumulonimbus tower develops as water vapor moves
from the surface to greater heights.
 Downdrafts form via entrainment (influx of cool dry air).
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Air-Mass Thunderstorms
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Stages of development:
Mature stage:
 This is the most intense phase.
 This results in heavy rain and possibly small hail.
 Cool downdrafts exist next to updrafts.

Dissipating stage:
 This stage is dominated by downdrafts and entrainment
causing evaporation.
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Air-Mass Thunderstorms
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Air-Mass Thunderstorms
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Occurrence:
 Mountainous regions, such as the Rockies and the
Appalachians, experience a greater number of air-mass
thunderstorms.
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Severe Thunderstorms
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Severe thunderstorms:
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Heavy downpours
Flash flooding
Straight line wind gusts
Hail, lightning
Wind shear
Can overshoot (enter stratosphere)
Downdraft preceding (gust front)
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Supercell Thunderstorms
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Supercell Thunderstorms
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Supercells
 These storms can produce extremely dangerous weather.
 They consist of a single, powerful cell that can extend to
heights of 20 km or more.
 The clouds can measure 20–50 km in diameter.
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Mesocyclone:
 Vertical winds may cause the updraft to rotate, which
forms a column of cyclonically rotating air.
 Tornadoes often form.
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Supercell Thunderstorms
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Squall lines:
 Squall lines are narrow bands of thunderstorms.
 cT air is pulled into the warm sector of a midlatitude
cyclone.
 Mammatus skies sometimes precede squall lines.
 These can also form along a dryline, where there is an
abrupt change in moisture.
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© 2011 Pearson
Supercell Thunderstorms
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Squall lines
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Supercell Thunderstorms
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Mesoscale convective complexes (MCC):
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An MCC consists of many individual thunderstorms.
It is organized into a large oval to circular cluster.
They cover an area of at least 100,000 km2.
It is a slow-moving complex that may last for 12 hours
or more.
 MCCs tend to form mainly in the Great Plains.
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© 2011 Pearson
Lightning and Thunder
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Lightning and Thunder
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What causes lightning?
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Lightning and Thunder
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Lightning strokes:
 The flash (total discharge) lasts a few tenths of a second.
 It is what we see and it contains multiple strokes.
 The leader is the ionized air, which forms a conductive
path.
 A step leader extends earthward in a short, nearly
invisible burst.
 The return stroke extends upward from ground to cloud.
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Lightning and Thunder
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Thunder:
 The air is heated quickly to as much as 33,000°C.
 It expands explosively, which produces sound waves that
travels at 330 mps.
 If lightning is more than 20 km away, thunder is not heard.
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Tornadoes
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Tornadoes (twisters, cyclones):
 These are violent windstorms with a rapidly rotating
column of air, or vortex.
 Pressures within tornadoes can be as much as 10% lower
than immediately outside the storm.
 It may consist of single or multiple vortices.
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Tornadoes
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The Development and Occurrence
of Tornadoes
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Tornado development
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The Development and Occurrence
of Tornadoes
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Tornado climatology:
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Squall lines
Cold fronts
Where cP and mT meet
Midwest U.S.
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The Development and Occurrence
of Tornadoes
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Profile of a tornado:
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Average diameter 150–600m
Travels ~45 kph
Path about 26 km long
Most travel to the NE
Exist between <3 min to >3 hours
Wind speeds between <150 kph to >500 kph
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The Development and Occurrence
of Tornadoes
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Tornado Destruction
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Tornado Destruction
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Tornado intensity
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Tornado Destruction
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Loss of life
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Tornado Forecasting
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Tornado watches and warnings:
 Watches alert the public.
 Tornadoes are possible and conditions are favorable.
 They usually cover an area of about 26,000 km2.
 Watches can last 3 hours or longer.
 Warnings are issued when a tornado is actually sighted or
conditions are just right.
 There is a high probability of imminent danger.
 They are usually for a much smaller area.
 Warnings are in effect for a much shorter period, usually
30–60 minutes.
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Tornado Forecasting
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Doppler radar
 This radar measures the motion and speed of the wind.
 Two or more units are optimal for more accurate
forecasting.
 Tornadoes have hooked-shaped echoes.
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© 2011 Pearson
Tornado Forecasting
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Doppler effect
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End Of Chapter 10
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