This document provides information about tornadoes. It begins by defining a tornado as a violently spinning column of air forming a vortex. Tornadoes typically form within supercell thunderstorms, which require wind shear, instability, moisture, and lift. The document explains how these conditions come together to create a mesocyclone and wall cloud from which a tornado may form. It notes that scientists understand tornado formation but continue to study why funnels descend from clouds. The summary concludes that while tornadoes are very destructive, increased scientific understanding has helped reduce annual deaths from 230 to around 70.
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Tornado Statistics
400 to 500 feet wide
1,000 feet tall
Winds are 112 miles per hour
Most less than ten minutes in duration
Only cover a few miles on the ground
6. Monster Tornadoes
Miles wide
Strongest winds ever
measured
Some 300 miles per hour
Can last for more than an
hour
Can travel over 200 miles
on the ground
6
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Tornado Alley
There are many
types of tornadoes,
but I will be talking
about the ones
in the Midwest in
an area called
“Tornado Alley”
8. Supercell
Largest, strongest, longest
lasting thunderstorms
They are huge rotating
thunderstorms
Create rain, hail,
dangerous wind, flash
floods & lightning and
sometimes, tornadoes
(up to 30% of the time)
8
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To understand how a tornado is
formed, we must first
understand Supercell
thunderstorms and the
conditions needed to create
them.
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I will first talk about the basic
elements,
and then show you how they all fit
together to form a tornado.
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Conditions
1. Warm moist air
Gulf of Mexico
2. Cold air Canada
and Polar
regions
3. Hot air South
Western desert
4. High winds of Jet
Stream
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Dry Line
Tornadoes form
along the boundary
where air masses
meet. Colliding air
masses at DRYLINE
trigger severe
storms which cause
tornadoes to occur.
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Wind Shear
Creates spinning columns of
horizontal wind:
Air moves at:
different speeds
different heights
different directions
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Instability
For a Supercell to
develop you also need
INSTABILITY
Warm air rises upwards
It is less dense than the
surrounding
atmosphere.
Rises like a hot air
balloon.
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Moisture and Latent Heat
Warm moist air rises and
cools.
Water vapor condenses
forming
Clouds
Condensation releases
latent heat (energy)
causing it to rise even
higher forming updraft
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Updraft
Sun warms ground,
ground warms air
Warm buoyant air
rises, breaking through
cooler air above
Vapor condenses,
releases heat, rises
higher, creating an
updraft
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Veering Winds
Veering winds turn
clockwise with height.
Turning winds with height
help thunderstorm
develop its most
essential component:
THE MESOCYCLONE
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Mesocyclone and Wind Shear
Wind shear (red) sets air spinning
The Updraft (blue) tilts spinning air
column upright
The updraft starts rotating
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Wall Cloud
Spinning layers of clouds
Descends from Mesocyclone
It is closer to
Mesocyclone’s
center
rain-free
Funnel cloud may form at
center
First stage of tornado
formation
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“Touching Down”
TORNADO MATURITY:
Mature at touch-down
Warm, moist air from
the ground continues
to fuels it making it
more powerful
Can last for minutes or
even an hour
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Tornado Losing Strength
Loses strength when cold
or dry air mixes with the
hot air that was fueling
the updraft
(The moist warm air is its
fuel)
Tornado spins into a
rope
whipping the
ground and disappears into
the air
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Tornado Losing Strength
As tornado dies, it tilts,
becomes ropelike, speeds
up, still destructive
Whips ground as it deflates
RFD that wrapped around
mesocyclone to form
tornado, eventually chokes
off inflow of warm air (fuel)
and kills it
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Summary
Tornadoes are earth’s most
destructive storms
3 out of 4 tornadoes happen in the
United States
Most tornadoes happen in the
Midwest in Tornado Alley
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Summary
Formed in Supercells - huge rotating
thunderstorms
Need Wind Shear, Instability, Moisture, and
Lift
Veering winds create essential component mesocyclone
Scientists uncertain why tornadoes spin
down
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In Conclusion
Scientists know a great deal about
the formation of tornadoes, but
they are difficult to study.
Once a tornado is gone, all they
can study is the damage it left
behind.
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The Fujita Scale estimates tornado
intensity based on damage - Rated from
F0 to F5.
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Before the National Weather
Service started studying tornadoes,
the average deaths a year, were
230 people.
Today, it’s dropped into the 70’s.
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The more we learn, the better
we can protect ourselves from
the most violent storm in the
world – A TORNADO!
Tropical air comes from the Gulf of Mexico. Hot, dry air from the desert. Where they meet is called the DRYLINE. This is where most tornadoes form.
1. The sun warm the ground. The ground warms the air above it. The hot, dry desert air traps or caps it. 2. It build up pressure.3. Eventually it breaks free forming an UPDRAFT resulting in thunderstorm within a cumulonimbus cloud
This is a cumulonimbus cloud. We will talk about this later
In this picture, winds are slower at the bottom level of atmosphere, but increase speed at higher level. Wind shear happens with winds at different speed, heights, and directions
Warm air rises into cooler atmosphere, creating clouds. These different temperatures create INSTABILITY
As warm moist air rises and cools, water vapor condenses forming clouds. This condensation releases latent (hidden) heat which is energy. This heats air, causing it to rise even higher forming an UPDRAFT
WARM AIR RISES BECAUSE IT IS LESS DENSE AND IS BUOYANT CAUSING AN UPDRAFT.
COOL AIR FALLS BECAUSE IT IS DENSER CREATING DOWNDRAFT
VEERING WINDS TURN CLOCKWISE WITH HEIGHT. TURNING WINDS CREATE THE SUPERCELL’S MOST ESSENTIAL COMPONENT: THE MESOCYCLONE
In the first picture you see rotating winds from WIND SHEAR. 2. The UPDRAFT tilts rotating air 3. until it is vertical.This is the MESOCYCLONE
A Wall cloud lowers from the MESOCYCLONE. This area is rain free. A funnel cloud may form here. This is the first stage of the formation of a tornado
This is another example of a wall cloud
Scientists believe the RFD circles around the mesocyclone, tightens it, and stretches it down to the ground. Supercells rise to the top of the troposphere and can go no further, so the air spreads out into an anvil shaped cloud
As the storm moves forward into the area where it has rained or hailed, there is no more warm, moist air to fuel the tornado. The tornado deflates and spins into a rope, whipping the ground and eventually disappears into the air.
Dies = tilts, ropelike, speeds up, still destructive. Some scientists believe that the same RFD that births the tornado, squeezes it, choking it until it dies dead
Scientists use the Fujita Scale to rate tornado intensity from an F0, the weakest, to F5 which is the strongest
