Watch out for flying cows

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Tornadoes

• Watch out for flying cows

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What is a tornado?

• A rapidly rotating column of air driven by energy
  in the atmosphere. Tornadoes develop from a
  supercell thunderstorm.

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Why do tornadoes form?

• Tornadoes develop from thunderstorms.
• When a cold front meets a warm front and forms a
  stationary front, a low pressure center can begin
  a counterclockwise rotation of air.
• An occluded front has the strongest convective
  forces that can give rise to a cyclone.

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Shearing winds disturb an air inversion.
Cold Dry Air Moving faster
Warm Dry Air Moving slower
Warm Moist Air Rising counterclockwise by convection
Westwind
South wind
whyfiles.org/013tornado/index.html
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When do tornadoes occur?

• April to June are the active months in the
  central plains states

• Summer tornadoes along the East Coast are usually
  associated with hurricane activity.

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Where do tornadoes occur?

• They are most common in the central United
  States, but can occur other places such at India
  and Bangladesh.

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Why do tornadoes occur there?

• Cold air from the polar regions and Rocky
  Mountains draws warm moist air out of the Gulf of
  Mexico.
• The westerly jet stream winds from the Rocky
  Mountains are called the Dry Line (shown in
  brown).
• Violent thunderstorms form with the cold dry air
  meets the warm moist air.

An occluded front forms.
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How are tornadoes measured?

• The Fujita Scale classifies tornadoes on wind
  speed and damage after the storm.
• Tornadoes are classified as F0 to F5.
• Large funnels cause widespread damage, but large
  pressure differences can cause extreme damage
  along a narrow path.

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whyfiles.org/013tornado/index.html
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The Importance of Pressure

• Low pressure is inside the cyclone at the core.
  High pressure is outside the cyclone.
• The greater the difference between the core
  pressure and the outside air pressure, the
  stronger the storm.
• Very low core pressure can cause a strong storm
  even with a small funnel width.
• Interactive Tornado

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End