Severe Weather

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Severe Weather
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Thunderstorms

• Small intense systems that can produce strong
  winds, rain, lightning and thunder.
• Need 2 conditions
• Air near surface needs to be warm and moist
• The atmosphere must be unstable

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Becoming unstable

• The surrounding air is colder than the rising air
  mass
• This makes that rising air CONTINUE rising
• The thunderstorm occurs when the air is rising
  rapidly
• Forms cumulonimbus cloud

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Lightning!

• Electrical charges build up near the tops and
  bottoms of clouds heading from positive to
  negative to positive (opposites attract)
• Flash of light occurs when a charge sparks
• The flash heats the air to about the temperature
  of the surface of the sun
• ENERGY IS RELEASED

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Effects

• Thunderstorms can have positive or negative
  effects
• Positive rain can provide water for crops and
  restore lakes and streams
• Negative
• Flash floods
• Winds
• Hail
• Lightning

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Funnel Cloud v. Tornado

• Wind traveling in 2 different directions causes
  it to start spinning
• The updrafts of air push the spinning column
  down, sometimes to the ground
• It is called a tornado once it hits the ground
• Funnel cloud Tornado

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Tornadoes

• Cumulonimbus clouds can sometimes form tornadoes
• Only 1 percent of thunderstorms form tornadoes

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Formation

• About 75 percent of tornadoes happen in the
  United States.
• Warm humid air comes up from the Gulf of Mexico
  and meets cold dry air from Canada in the plains.
  

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Effects

• Winds usually average around 95mph
• Most are small and last only a few minutes
• Larger ones are less common (20) are strong
  enough to knock over trees, lift cars or take
  roofs off houses.
• Very few (1) are violent enough to lift or
  completely demolish sturdy buildings and can last
  more than two hours

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Path

• A tornado moves along with its thunderstorm, it
  travels fast and weaves a path that is impossible
  to predict
• Tornado watch
• When the weather conditions might produce
  tornadoes.
• Tornado warning
• When a tornado has
• been detected

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Hurricanes

• Most powerful storms on Earth
• Different names
• Typhoons Pacific Ocean
• Cyclones Indian Ocean
• Form over warm tropical oceans
• 5o 20o North and South
• Vary in size
• 160 km to 1,500 km in diameter
• Can travel thousands of miles

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Formation of Hurricanes

• Hurricane Season August to October
• Begins as a group of thunderstorms
• Energy
• Comes from condensed water vapor
• Energy moves from ocean water into the air
• Strong Winds Develop
• Coriolis effect bends the wind
• Fuel
• Direct contact with warm ocean water
• Hurricanes will continue to grow until they lose
  their source of warm, moist air

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Hurricane Features
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Effects of Hurricanes

• Wind Speed
• 120 km/h to 300 km/h
• Can cause damage in a variety of ways
• Lift Cars
• Produce tornadoes
• Uproot Trees
• Tear roofs off buildings
• Heavy rains cause rivers to overflow
• When a hurricane moves into a coastal area it
  causes a storm surge
• Storm surges can rise sea level and have large
  waves (1m to 8m)
• National Hurricane Center tries to warn people in
  time.

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Winter Storms

• Formed when two air masses collide.
• A continental polar air mass forming over snow is
  especially cold, dry, and dense.
• It forces moist air to rise very quickly.

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Blizzards

• A storm with falling or blowing snow, winds at
  least 35 mph, reduced visibility and intense
  cold.
• Occur in many parts of the Northern and Central
  United States.

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Formation of a Blizzard

• When warm air collides with cold air and is
  forced to rise above the colder air, the warm air
  brings moisture.
• This moisture is formed normally by the wet air
  moving from the South or by blowing across large
  bodies of water.
• A lift is created to raise moist air to form
  clouds and create ice and snow.

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Duration of a Blizzard

• For a storm to be considered a blizzard it has to
  last at least 3 hours.
• Some blizzards can last for a few hours or even
  days!

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Dangers of Blizzards

• Whiteout conditions make it hard to see when
  traveling.
• Strong winds and cold temperatures can create
  dangerous wind chill temperatures.
• Roads can be slippery to drive on.
• Power outages can occur due to strong winds and
  heavy snow.
• Pipes can freeze and fuel
• sources can be cut off.

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Dust Storm

• Strong, violent winds that carry fine particles
  like silt, clay, sand and dust-filled air over an
  extensive area.

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Formation of a Dust Storm

• Any area with a lot of dust and sand particles
• Need dry air No precipitation or water vapor in
  the air
• Lots of wind
• Huge
• Can spread over hundreds of miles
• Powerful
• Wind speeds of at least 25 miles per hour (40 km)

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Dangers of a Dust Storm

• Arrive without warning
• Create large wall of dust and debris.
• Last only a few minutes
• Leave debris behind
• Hard to see during storm
• Breathing is impacted.
• Takes fertile top soil away and reduces future
  crops.
• Current crops are covered with dust.