thunderstorms · 2015. 2. 20. · thunderstorms •heavy rainfall with thunder and lightning....
TRANSCRIPT
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Thunderstorms
2009
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Storms • A violent
disturbance in the atmosphere.
• Involve sudden changes in air pressure, which cause rapid air movement.
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Thunderstorms • Heavy rainfall with
thunder and lightning.
• Form within cumulonimbus clouds.
• Warm air rapidly rises, causing updrafts that bring moisture to the tops of the cloud.
• The moisture condenses, and eventually forms rain.
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TS Ingredients
• Thunderstorms need three things:
• Moisture - to form clouds and rain.
• Unstable Air - relatively warm air that can rise rapidly.
• Lift - fronts, sea breezes and mountains are capable of lifting air to help form thunderstorms.
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When Do Ts Occur?
• Most likely to occur in the spring and summer months and during the afternoon and evening hours.
• Can occur year-round and at all hours of the day or night.
• Along the Gulf Coast and across the southeastern and western states, most thunderstorms occur during the afternoon.
• Thunderstorms often occur in the late afternoon and at night in the Plains states.
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Facts
• Thunderstorms affect small areas when compared with hurricanes and winter storms.
• The typical thunderstorm is 15 miles in diameter and lasts an average of 30 minutes.
• Nearly 1,800 thunderstorms are happening at any moment around the world.
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Life Cycle of thunderstorms
• All thunderstorms, whether or not they become severe, progress through a life cycle which may be divided into three main stages
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Developing Stage
• Moist air, heated by the sun, rises which causes an updraft of air.
• As warm air rises, it cools and forms clouds. As the water vapor condenses it gives its energy to the surrounding air, making it warmer and causes it to rise more. This energy powers the thunderstorm.
• Usually little if any rain during this stage.
• Lasts about 10 minutes • Occasional lightning
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Mature Stage
• Most likely time for hail, heavy rain, frequent lightning, strong winds, and tornadoes.
• Storm occasionally has a black or dark green appearance
• Lasts an average of 10 to 20 minutes but may last much longer in some storms.
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Dissipating Stage
• Rainfall decreases in intensity
• Can still produce a burst of strong winds
• Lightning remains a danger • When the downdrafts in the
cloud begin to dominate over the updrafts, this happens
• Since warm moist air can no longer rise, cloud droplets can no longer form
• The storm dies out with light rain as the cloud disappears from bottom to top
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Thunderstorm Stages
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Single-cell Thunderstorm
• A single, isolated
thunderstorm
• Have a lifespan of
about 30 minutes
• Are not very severe
• Very rare and occur
randomly
• Are difficult to
forecast
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Multi-cell Cluster Storms
• Are the most common
type of thunderstorms
• Occur in a group
• Persist for a few hours
• Produce modern size
hail
• Weak tornadoes occur
during this storm
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Multi-cell Line storm
• Consists of long line thunderstorms usually associated with fronts.
• Can produce hail the size of golf balls
• Weak tornadoes
• Can easily be predicted with the help of radar
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Super Cell
• Although rare, highly organized thunderstorms
• Pose of high threat to life and property, as
these can produce strong to violent tornadoes
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Thunder and Lightning • Friction between
updrafts and downdrafts cause electrons to be stripped from some atoms and given to others. Just like walking across a carpet in your socks.
• So the clouds develop charges.
• Lightning is the spark when the discharge occurs.
• Lightning is one big static electricity discharge!
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What Causes Lightning?
• In a cloud, swift air
separates water droplets,
causing electrical
charges.
• The electrical charges
build up and causes huge
electric shocks. It
generates about 100
million volts of electricity.
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Thunder
• Thunder is caused by lightning.
• When a lightning bolt travels
from the cloud to the ground it
actually opens up a little hole in
the air, called a channel.
• Once then light is gone the air
collapses back in and creates a
sound wave that we hear as
thunder.
• The reason we see lightning
before we hear thunder is
because light travels faster than
sound!
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How Far Away?
• Sound travels roughly 1-km in 3 seconds or 1-mile in 5 seconds.
• So if you see the flash of lightning, and it takes 10 seconds for the thunder to reach you, the lightning was about 2 miles away.
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Forked Lightning
• Forked lightning: Bolts that most commonly occur between clouds and the earth.
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Ball Lightning
• Ball lightning:
• A very rare.
• It is a sphere shape
that glows and
moves slowly.
• It forms in a storm
cloud, and can last
five seconds.
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Heat Lightning
• Heat - Lightning from
storms that are so far
away that we can't
hear the thunder or
see any rain.
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Sheet Lightning
• Sheet Lightning: covers a wide area, and can be inside or
between clouds.
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Thunderstorm Safety • Go inside! • Get in car if you can’t make it to
a sturdy building (basements are good).
• If caught outside, stay away from tall objects like trees.
• Make sure that you are not the tallest object by crouching down. Crouch down, bend forward, and grab your ankles. Keep your head down. Do not lie flat on the ground and try to keep out of puddles or other standing water.
• Do not use a phone or a computer during a thunderstorm.
• Do not take a shower or wash dishes.
• If there are downed power lines anywhere around you, DO NOT touch them
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Thunderstorm Watch/Warning
• Severe Thunderstorm
Watch -conditions are
conducive to the
development of severe
thunderstorms in and
close to the watch area.
• Severe Thunderstorm
Warning - a severe
thunderstorm has
actually been observed
by spotters or indicated
on radar, and is
occurring or imminent in
the warning area. Time
to take cover!