Chapter 20.3 Severe Storms

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Chapter 20.3 Severe Storms Tornadoes!
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Thunderstorms!

• A storm that generates lightning and thunder.
• Frequently produces gusty winds, heavy rain, and
  hail.

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Thunderstorms!

• Occurrence of thunderstorms
• At any given time, there are an estimated 2,000
  thunderstorms in progress on Earth!
• The greatest number occur in the tropics where
  warmth, plentiful moisture, and instability are
  common atmospheric conditions.

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Thunderstorms!

• Development of thunderstorms
• Form when warm, humid air rises in an unstable
  environment.

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Stages in the Development of a Thunderstorm
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Tornadoes

• Tornadoes
• violent windstorms in the form of a rotating
  column of air called a vortex.
• The vortex extends downward from a cumulonimbus
  cloud.

Vortex Shape
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• Occurrence and Development of Tornadoes
• A mesocyclone is a vertical cylinder of rotating
  air that develops in the updraft of a
  thunderstorm.

Stage 1
Stage 2
Stage 3
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Tornado Anatomy

• Anvil - Updrafts cause cumulus clouds to grow
  into towering mountains called cumulonimbus
  clouds. This cloud typically hits the
  stratosphere, which acts like a ceiling. This
  forces the cloud to spread sideways and form a
  distinctive anvil shape.
• Wall Cloud - Tornadoes tend to form under a wall
  cloud, a smaller cloud underneath the main cloud.
  It is relatively free of precipitation and
  sometimes helps storm spotters visually identify
  where a possible tornado might hit the ground.
• Precipitation - Precipitation follows a fairly
  specific pattern Light rain, heavy rain, light
  hail and finally large-sized hail. Generally, the
  wall cloud area around the tornado is
  precipitation-free (although in example on the
  next slide hail was falling behind the tornado)
• Flanking Line - The back of a massive
  thunderstorm usually has a flanking line of stair
  or finger like cumulus cloud towers. The wall
  cloud is usually found underneath the area where
  the flanking line intersects the tallest-growing
  tower in the storm.

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Tornadoes

• Tornado Intensity
• Tornado winds cannot be measured directly, so a
  rating on the Fujita scale is determined by
  assessing the worst damage produced by the storm.

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Tornadoes

• Tornado Safety
• Tornado Watch alert people to the possibility of
  tornadoes in a specified area for a particular
  time.
• Tornado Warning issued when a tornado has
  actually been sighted in an area or is indicated
  by weather radar.

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Tornado Damage Madison Indiana
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Tornado on the southwest side of Indianapolis on
May 30, 2004
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Tornado touched down in Indianapolis on June 11,
2004
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June 9, 2005 in Hill City, Kansas
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Tornado Damage