Severe Weather

1
Severe Weather

• Some Meteorology Basics

2
Atmospheric Heating

• Atmosphere is heated from the bottom
• Solar energy absorbed by the Earth is re-radiated
  as heat
• Warm air is less dense so it rises
• This mixing of the air produces our weather

3
Atmospheric Heating is Uneven

• Latitude (position relative to the poles and the
  equater) influences amount of solar energy
  received
• Land re-radiates heat much faster than water
• Moisture also plays a role
• Evaporation requires energy
• Condensation releases energy

4
Uneven Heating and Air Pressure

• Areas where air is heated
• Air becomes less dense (weighs less)
• Air rises
• Combination is measured as Low Pressure

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Uneven Heating and Air Pressure

• Areas where air is less heated
• Air becomes more dense (weighs more)
• Air sinks
• Combination is measured as High Pressure

6
Air Pressure and Weather

• Low Pressure areas have rising air
• Air rises to areas where it is cooler
• Cooling may produce condensation
• Condensation may result in precipitation
• Lows are generally associated with stormy weather

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Air Pressure and Weather

• High Pressure areas have sinking air
• Air sinks to areas where it is warmer
• As air is heated, it can hold more moisture
• If more moisture is not available, the effect is
  that the air become drier (less humid)
• Highs are generally associated with clear weather

8
Air Pressure and Wind

• Warm air rises in areas of Low Pressure
• Cool air sinks in areas of High Pressure
• To equalize the pressure, air must move from
  areas of High Pressure to areas of Low Pressure
• This movement of air is called wind

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Simple, but not so simple

• Air moves from areas of high pressure (sinking)
  to areas of low pressure (rising)
• However, the air doesnt follow a straight path
• Because the Earth spins on its axis, the wind is
  deflected in a slightly different direction

10
Coriolis Effect

• The deflection of the wind, or any moving
  object, because of the Earths rotation is known
  as the Coriolis Effect
• In the Northern Hemisphere, moving objects are
  deflected to the right of their intended path

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Highs, Lows and Around It Goes

• Wind blows from High Pressure toward Low Pressure
• We can also think of this as blowing outward or
  away from the High
• And, inward or toward the Low
• The Coriolis Effect deflects these winds, so

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Highs, Lows and Around It Goes

• Winds blow clockwise and out from Highs
• Winds blow counterclockwise and in toward Lows

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Counterclockwise winds around a Low Hurricane
Fran
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Counterclockwise winds around a Low The Perfect
Storm
15
Low Pressure andSevere Weather

• Air rises, cools and may promote condensation in
  Lows
• Lows are generally associated with stormy weather
• Some storms are quite severe

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Examples of Severe Weather and Low Pressure
Systems

• Tropical Depressions (Lows)
• Tropical Storms (Stronger Lows)
• Hurricanes (Very Strong Lows)
• Mid-Latitude Cyclones (Strong Lows with
  associated warm and cold fronts)
• Noreasters (Strong Lows that move off the East
  Coast
• Tornadoes (Small, powerful Lows associated with
  fronts)