http://www.youtube.com/watch?v=jM8h60S1GsM
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Severe weather is
weather that can cause
property damage and
sometimes death
Examples of severe
weather are:
Thunderstorms
Tornadoes
Hurricanes
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Thunderstorms are
small, intense weather
systems that produce
strong winds, heavy
rain, lightning and
thunder.
Thunderstorms can
occur at cold fronts.
 There are only two
atmospheric
conditions required to
produce
thunderstorms:
 Warm, moist air near
the Earth’s surface
 An unstable
atmosphere.
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The atmosphere is
unstable when the
surrounding air is colder
than the rising air mass.
The air mass will
continue to rise as long
as the surrounding air is
colder than the air mass.
When the warm rising air
reaches its dew point,
the water vapor
condenses and forms
cumulus clouds
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If the atmosphere is
extremely unstable,
the warm air will
continue to rise, which
will cause the cloud to
grow into a dark,
cumulonimbus cloud.
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Thunderstorms can be
active electrically.
http://www.youtube.com/
watch?v=G7GbOFlFODE
Lightning is an electric
discharge between a
positively charged area
and a negatively charged
area.
Lightning can happen
between two clouds, the
Earth and a cloud, or even
between two parts of the
same cloud.
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When lightning strikes,
energy is released.
 This energy is
transferred to the air,
and the heated air
expands rapidly,
sending out sound
waves.
 Thunder is the sound
that results.
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Severe thunderstorms can produce one or more of the
following conditions:
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High winds
Hail
Flash floods
Tornadoes
Tornadoes only happen in
about 1% of all
thunderstorms.
 A tornado is a rapidly
spinning, column of air that
has high wind speeds and low
pressure.
 http://www.youtube.com/wat
ch?v=S-UPAcKNvII
 Tornadoes start as a funnel
cloud that pokes through the
bottom of a cumulonimbus
cloud, when/if the funnel
cloud touches the ground, it
becomes a tornado
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About 75% of all
tornadoes on Earth
happen in the US
 Most occur in the
spring or early summer
 Cold, dry air from
Canada meets up with
warm, moist air from
the tropics
 Wind speeds average
120 mph
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Hurricanes are large,
rotating, tropical weather
systems with wind speeds
of at least 75 mph.
Hurricanes are the most
powerful storms on Earth.
http://www.youtube.com/
watch?v=4f45jA5UxB0
Hurricanes develop near
the equator between 5*
and 20* North and South
latitudes over warm,
tropical oceans
A hurricane begins as a
group of
thunderstorms that
move over tropical
waters.
 Winds moving in
different directions
meet and cause the
storm to spin.
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A hurricane gets its energy from
the condensation of water vapor.
The warm water of the ocean
provides fuel for the hurricane.
Moisture is added to the warm
air by evaporation from the
ocean.
As the warm, moist air rises, the
water vapor cools and
condenses and releases huge
amounts of energy.
As long as the hurricane has
warm water as fuel, it will
continue to grow
Once it passes over land or
colder waters, it will begin to die
as it loses its source of energy