Severe Weather

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Severe Weather

• Chapter 25

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Midlatitude Cyclones

• Areas of low pressure characterized by rotating
  wind that moves toward the rising air of the
  central, low-pressure region.
• Last several days
• Pass from Pacific coast to Atlantic coast
• Strongly influence weather in middle latitudes
  (us!)

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Stages of a Midlatitude Cyclone (Page 607, Figure
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Thunderstorms

• Rain
• Strong Winds
• Lightning
• Thunder

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Stages in Thunderstorm Development

• Stage 1Cumulus Stage
• Air rises, condenses, forms cumulus cloud
• Stage 2 Mature Stage
• Becomes Dark Cumulonimbus Cloud, heavy rains
  cause down drafts
• Stage 3 Dissipating Stage
• Downdrafts end updrafts, storm loses moisture,
  storm dissipates

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Lightning Formation
Lightning forms due to the attraction of opposite
electrical charges
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Tornadoes

• Smallest. Shortest, and most violent storms.
• Forms when a thunderstorm meets high altitude
  horizontal winds
• Winds cause rising air to rotate

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Other Tornado Characteristics

• Usually cover paths lt100m wide
• They have occurred in all 50 states
• Most common in Tornado Alley
• Winds greater than 400 km/h

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Enhanced Fujita Scale (EF Scale)

• Adopted Feb. 1st, 2007
• Takes into account damage and wind
• Link to NOAA website
• March 12th, 2006, Springfield, IL