Transcript Severe Weather Thunderstorms, Tornadoes, Hurricanes, etc…

Severe Weather
Thunderstorms, Tornadoes,
Hurricanes, etc…
In this section, we will learn…
Tornadoes, hurricanes, blizzards, and thunderstorms are severe
weather phenomena that impact society and ecosystems. Hazards
include downbursts (wind shear), strong winds, hail, lightning,
heavy rain, and flooding.
The movement of air in the atmosphere is due to differences in air
density resulting from variations in temperature. Many weather
conditions can be explained by fronts that occur when air masses
meet.
• E4.3A Describe the various conditions of formation associated with severe
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weather (thunderstorms, tornadoes, hurricanes, floods, waves, and
drought).
E4.3B Describe the damage resulting from and the social impact of
thunderstorms, tornadoes, hurricanes, and floods.
E4.3C Describe severe weather and flood safety and mitigation.
E4.3D Describe the seasonal variations in severe weather.
E4.3E Describe conditions associated with frontal boundaries that result in
severe weather (thunderstorms, tornadoes, and hurricanes).
Thunderstorms
• Thunderstorms are most often
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associated with a Cumulonimbus
Cloud
This is a cloud that forms when air
is forced high into the atmosphere
(against its will)
Cold fronts often create this
condition
This produces an UNSTABLE
environment
The process of cooling, condensing,
cloud formation, saturation and
precipitation occurs quickly
Cold fronts often create the proper
conditions for this to occur
Thunderstorm Formation
• Thunderstorms have three stages…
– The Cumulous Stage: Warm air rising and condensing to form
clouds
– The Mature Stage: Strong updraft of warm, moist air, AND a
strong downdraft of wind and precipitation (hail and lightning can
occur in this stage too)
– The Dissipation Stage: The surface has been cooled, cutting
off the warm, moist air that “fuels” the storm. Once the
precipitation has fallen from the sky, the storm is over
Lightning
• Lightning is believed to be
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created by friction between
the rising updraft and the
falling downdraft in a
cumulonimbus cloud
This friction creates a
separation of charges (kinda
like rubbing your feet across
the carpet in your socks)
Eventually there is a discharge
between positive and negative
charges, creating a “spark”
(kinda like touching that
doorknob and getting a
shock)
On a larger scale, that “spark”
is a bolt of lightning
Thunder
• When lightning strikes, the “bolt” can
be as hot as 30,000 degrees
• The air surrounding that bolt of
electricity expands rapidly
(remember… warm air expands), and
then contract quickly as it cools.
• Because of the extremely high
temperatures involved, the air
expands and contracts rapidly
enough to break the sound barrier
(767 mph)
• The thunder is a “sonic boom”
Wind & Downdrafts
• What goes up, must come
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down!
Thunderstorms are no
different, when warm air
rises high into the
atmosphere, it eventually
cools and comes back down
toward the surface
Cumulonimbus clouds can
be as tall as 40,000 feet,
so…
It can fall very quickly
toward the surface,
producing strong winds
(called downdrafts)
Hail
Tornadoes
Thought to be the 1st photograph of a tornado (1884)
Tornadoes
• Violent windstorms that take
the form of a rotating column
of air, or vortex, that extends
downward from a
cumulonimbus cloud.
• Because of the lower pressure
in the center vortex, air near
the ground rushes into the
tornado from all directions.
• Air streams inward, it is
spiraled upward around the
core until it eventually merges
with the airflow or the parent
thunderstorm deep in a
cumulonimbus tower.
Tornadoes
• Some tornadoes consist of a
single vortex.
• However, within many stronger
tornadoes are smaller intense
whirls known as suction
vortices, that orbit the center of
the larger tornado → Multiple
Vortex Tornadoes.
– Usually die out in less than a
minute.
Tornadoes
• Suction vortices are
responsible for most
of the narrow, short
waves of extreme
damage that
sometimes are
through tornado
tracks.
– Most reports of several
tornadoes at once
actually were multiple
vortex tornadoes.
Supercell Structure
Tornado Development
• Less than 1% of
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thunderstorms produce
tornadoes.
Most intense tornadoes
are associated with
supercells (big,
cumulonimbus cloud
structures).
• Tornado formation begins
with the development of
a mesocyclone.
– Mesocyclone- Vertical
cylinder of rotating air
that develops in the
updraft of a severe
thunderstorm.
Tornado Development
Tornado Development
• The mesocyclone within
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the cloud stretches
vertically and narrows
horizontally, causing
winds speeds to
accelerate.
Air stretches downward
until a portion of the
cloud protrudes below the
cloud base, producing a
dark, slow rotating wall
cloud.
*See supercell diagram for
Tornado Classification
• Fujita Intensity Scale–
Assesses the damage produced
by a storm as it relates to wind
speed.
• F0- Moderate; 40-72 mph
• F5- Severe; 261-318 mph
– Path of Destruction
– Duration
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account for structural integrity of
objects.
The ENHANCED Fujita Scale (EF –
Scale) is now used in the US. It
DOES take into account structural
damage (but still uses a 0-5
numerical scale)
Watches & Warnings
• Tornado Watch
– Conditions are ideal for
a tornado to be
created.
• Tornado Warning
– An actual tornado has
been sighted in the
area or is indicated by
weather radar.
Tornado Frequency in the US
Tornado Frequency Around the
World
Cool Tornado Pictures
Hurricanes
Hurricane Formation
• The hurricanes that strike
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the Caribbean, Gulf of
Mexico and the US
originate in Africa
They begin as low
pressure storm systems
over land
The Trade Winds (one of
the systems of global
winds) blow them out over
the warm water of the
Atlantic Ocean
Hurricane Growth
• Remember that low pressure
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pulls air in at the surface…
and pushes it to higher levels in
the atmosphere
Air temperatures at high levels
in the atmosphere are colder,
and the warm, moist air over
the ocean begins to form clouds
(BIG Cumulonimbus clouds)
Lots of Latent Heat released
during condensation
Creates a very unstable
environment
Continued Growth
• Remember that the water
over the Atlantic Ocean
near Africa is warm (80°F)
and has lots of moisture in
it (mT air masses)
• As precipitation begins,
the rain and cool
downdrafts of the
Cumulonimbus system are
not enough to cut off the
updraft (it’s too warm)
• The warm, moist air
continues to fuel the
system of Cumulonimbus
clouds, making them
bigger, and bigger, and
bigger
Hurricane Movement
• Once the growing low
pressure system is out
over the warm water of
the Atlantic Ocean, the
Trade Winds blow it to
the west
• Because the oceans are
relatively smooth, there
isn’t much to stand in its
way and slow it down
• With 2,000 to 3,000 miles
of warm ocean water to
move across…
• the system has the time
and the fuel to become
severe
Tropical Depressions, Tropical
Storms and Huricanes
• Low pressure begins as a Tropical Disturbance
• The low pressure systems that blow out over the waters of
the Atlantic Ocean begin as Tropical Depressions (a low
pressure system is in fact a “depression” of pressure)
• If winds in the system reach 39mph, the system becomes
classified as a Tropical Storm (and it is given a name)
• If the system continues to gain strength and winds speeds
reach 74 mph, it is officially classified as a hurricane
Hurricanes, Typhoons and Cyclones
• We give different
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names to Tropical
Storms that develop,
depending on their
location
In the Atlantic Ocean
we call them
Hurricanes
In the Pacific Ocean we
call the Typhoons
In the Indian Ocean we
call them Cyclones
They are all basically
the same type of storm
Hurricane Dangers
• The most dangerous
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component of a hurricane is
the “Storm Surge”
As the storm makes landfall,
a mound of ocean water
(driven by strong winds AND
the “sucking” power of the
strong low pressure system)
is pushed on shore
More people die as a result
of drowning, than do of
strong winds
Hurricane Classification
The Safir-Simpson Scale
Type
KNOTS
MPH
millibars
inches of
mercury
Feet
Meter
s
Damage
Depression
less than
34
less than
39
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Tropical
Storm
35 - 63
39 - 73
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Category 1
64 - 82
74 - 95
greater than
980
greater than
28.94
3-5
1.0 1.7
minimal
Category 2
83 - 95
96 - 110
979 - 965
28.50 - 28.91
6-8
1.8 2.6
moderate
Category 3
96 - 113
111 - 130
964 - 945
27.91 - 28.47
9 - 12
2.7 3.8
extensive
Category 4
114 - 135
131 - 155
944 - 920
27.17 - 27.88
13 18
3.9 5.6
extreme
Category 5
136+
156+
less than 920
less than 27.17
19+
5.7+
catastrophic
A Hurricane’s “Death”
• As a hurricane makes
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landfall, the supply of
warm, moist air that was
fueling it is cut off
As the downdrafts and rain
cool the land, the strength
of the updraft slows
Without an updraft, the
system will dissipate, and
eventually die out (just like
a thunderstorm)
This may take days and
100’s of miles
Hurricane Ike comes to
Michigan in 2008 (my front
yard in Commerce
Township) >
Hurricane Katrina
• In August of 2005, Tropical
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Storm Katrina developed over
the Bahamas
As it approached Florida, it
developed into a Category I
hurricane
It lost some strength over the
land (turned back into a
Tropical Storm), but picked
right back up when it moved
back over the warm water of
the Gulf of Mexico
Hurricane Katrina
• As the storm moved across
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the Gulf of Mexico, it
RAPIDLY developed
(from a Category II to a
Category V in only 9
hours)
Wind speeds reached 175
mph
A mound of water was
pushed toward Louisiana
and Mississippi…
even though wind speeds
slowed (to a Category III)
by the time it made
landfall
Flooding
• While the storm surge
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associated with Katrina
was estimated to be 28
feet above normal sea
level
In addition, much of the
city is BELOW sea level
A systems of levees and
dams were supposed to
protect the city, but this
was too high
85% of the city flooded
The Aftermath
• The most destructive and
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costliest natural disaster in the
history of the US
More than $81 billion dollars in
damage
More that 1800 people died
(700 still listed as missing)
More than 90,000 square miles
declared a Federal Disaster
Area
More than 3 million people
were left without power
In Addition…
• There were unforeseen
economic effects
– Gas and Oil production
shut-downs
– Unemployment
– Insurance Company
Bankruptcies
– Relocation/Flight from the
region
• Environmental Effects
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Oil Spills
Erosion
Sewage
Loss of Marine and Animal
life
• Looting and Violence