Thunderstorms and Tornadoes

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Thunderstorms and Tornadoes

• By Bisma Parvez, Teri-Lynn Gelinas,
• and Lydia Kim

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What are Tornadoes?

• A tornado is a violent windstorm characterized
  by a twisting, funnel-shaped cloud.
• It is spawned by a thunderstorm (or sometimes as
  a result of a hurricane) and produced when cool
  air overrides a layer of warm air, forcing the
  warm air to rise rapidly.

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How Tornadoes are Formed

• Tornadoes are formed because thunderstorms
  usually contain updrafts, which are large rising
  swells of warm, moist air.
• As the updraft moves, it rotates if the rotation
  grows sufficiently intense, the storm can evolve
  into a tornado or funnel cloud

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What Time of Year it Occurs

• Tornado season is generally March through August,
  although tornadoes can occur at any time of year.
• Most tornadoes occur during the mid afternoon to
  early evening. They can occur at anytime and
  without any warning.

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Which Area is Most Common?

• In the United States, most tornadoes occur in the
  area of Texas, Kansas, Nebraska, Iowa, and
  Oklahoma. This area is known as the Tornado
  Alley.
• Canada's "tornado alleys" are southern Ontario,
  Alberta, southeastern Quebec, and a band
  stretching from southern Saskatchewan and
  Manitoba through to Thunder Bay.

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Tornadoes in This Area

• Windsor, Ontario- June 17, 1946 17 dead,
  hundreds injured
• Windsor, Ontario-April 3, 1974 9 dead, 30
  injured
• Barrie, Ontario- May 31, 1985 8 dead, 155
  injured

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Recent Tornadoes

• November 10, 2002 850 PM CSTAbout one third of
  the town of Carbon Hill, Walker County, Alabama,
  was completely destroyed. At least 11 people were
  killed and 50 were injured. The tornado ripped
  through the very center of town.
• November 10, 2002 745 PM CSTIn Lowndes County,
  Mississippi, one man was killed when a tornado
  threw his trailer 150 feet. The same tornado, or
  one in the same family, destroyed dozens of
  buildings at Columbus.

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Recent Tornadoes Continued

• November 5, 2002 600 PM CSTA tornado disrupted
  the election process in Abbeville, Alabama. The
  funnel ripped apart homes, businesses, and the
  high school in the downtown area. One person died
  as a large tree crashed through the house. About
  25 others were injured.

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Potential for Destruction

• Every tornado is a potential killer and may cause
  considerable damage.
• The most violent tornadoes are capable of
  tremendous destruction with wind speeds of 250mph
  or more.
• Damage paths can be in excess of one mile wide
  and 50 miles long.

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Frequency

• On average, there are about 850 tornadoes per
  year.
• In 1973 1990 there were over 1100 tornadoes
  reported.
• In Canada, during an average year, there are
  about 80 tornadoes.

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Other Exciting Details

• Tornadoes vary in size from a few hundred yards
  wide to over 20 miles.
• Most rotate counter-clock-wise in the northern
  hemisphere and clockwise in the southern
  hemisphere because of the Coriolis effect.
• Most move from southwest to northeast, however,
  their direction can be very erratic. The time a
  tornado spends on the ground may vary from a few
  minutes to many hours.

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What are Thunderstorms

• Thunderstorms are relatively small, organized
  parcels of warm and moist air that rise and
  produce lightning and thunder. They are one of
  Nature's frequent ways of balancing the amount of
  energy in the atmosphere - it is estimated that
  over 40,000 thunderstorms occur each day around
  the world.
• a cumulonimbus cloud that reaches sufficient
  intensity to produce lightning and thunder.

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How it Forms

• The basic fuel is moisture (water vapour) in the
  lowest levels of the atmosphere. The air above
  the lowest levels has to cool off rapidly with
  height, so that 2-3 miles above the ground, it is
  very cold.

• Finally, we need something in the atmosphere to
  push that moist air from near the ground up to
  where the air around it is cold. This "something"
  could be a cold front or the boundary between
  where the cold air from one thunderstorm meets
  the air outside of the storm or anything else
  that forces the air at the ground together.

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The Time of Year it Occurs

• The best time of year for a thunderstorm to occur
  is between September to March.
• While most of the more violent storms occur in
  the spring and summer months, thunderstorms may
  develop at any time of the year.

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Where it is Most Common

• The Midwest and Great Plains regions of the U.S.
  average between 40 and 60 days of thunderstorms
  per year. These two regions are prone to some of
  the most severe thunderstorms on Earth.
• Florida experiences an average of 90 days or more
  per year of thunderstorm activity. This is mostly
  due to the proximity to the Gulf of Mexico and
  the Atlantic Ocean, which provide an ample amount
  of warm, moist air.

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Thunderstorms in Our Area

• Tuesday July 23, 2002 - Thunderstorms in southern
  Ontario knocked down power lines and ruptured gas
  lines.
• Severe thunderstorms, stretching from Barrie to
  Windsor, moved through southern Ontario on Monday
  July 22, 2002.

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Potential For Destruction

• Severe thunderstorms are really dangerous. They
  are capable of producing baseball sized hail,
  strong winds, intense rain, flash floods, and
  tornadoes. Severe thunderstorms can last several
  hours and grow 18km high.

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Frequency

• Its estimated that 100,000 thunderstorms occur
  each year in the U.S.
• World wide, the tropics produce by far the most
  thunderstorms. On a daily basis, about 44000
  thunderstorms occur and about 2000 are in
  progress at any time.

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Other Exciting Details

• There are three stages describing the life cycle
  of an air-mass thunderstorm.
• 1. cumulus
• 2. mature
• 3. dissipating
• About 10 of the thunderstorms that occur each
  year in the United States are classified as
  severe.
• They may appear different in
• colour and some may not be seen.

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