Tornadoes

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Tornadoes

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Tornadoes

  1. 1.  A tornado is a violent rotating column of air extending from a thunderstorm to the ground  Most tornadoes form from thunderstorms.  You need warm, moist air from one direction and cool, dry air from another direction. When these two air masses meet, they create instability in the atmosphere.  Next, a change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere.  Rising air tilts the rotating air from horizontal to vertical.  When talking about tornadoes in the US (where the majority of tornadoes occur), the warm air comes from the Gulf of Mexico and the cool, dry air comes from Canada.
  2. 2. 1) The rotating cloud base lowers 2) This lowering cloud becomes a funnel, which continues descending while winds build near the surface, kicking up dust and other debris. 3) Finally, the visible funnel extends to the ground, and the tornado begins causing major damage. 4) This tornado, near Dimmitt, Texas, was one of the best- observed violent tornadoes in history.
  3. 3.  Tornadoes can happen at any time of the year and at any time of the day.  In the southern US, peak tornado season is from March through May, when there are strong winds and atmospheric instability.  Peak times for tornadoes in the northern states are during the summer.  Tornadoes are least common in the winter  Tornadoes are most likely to occur between 3 p.m. and 9 p.m.
  4. 4.  The Great Plains (the central US): has all the necessary ingredients for tornadoes.  More than 500 tornadoes typically occur in this “Tornado Valley” every year  Other areas of the world that have frequent tornadoes include South Africa, parts of Argentina, Paraguay, and southern Brazil, as well as portions of Europe, Australia and New Zealand, and far eastern Asia.
  5. 5.  There are several different scales for rating the strength of tornadoes.  The Fujita Scale rates tornadoes by damage caused  An F0 or EF0 tornado, the weakest category, damages trees, but not substantial structures. An F5 or EF5 tornado, the strongest category, rips buildings off their foundations and can deform large skyscrapers.  The similar Torro Scale ranges from a T0 for extremely weak tornadoes to T11 for the most powerful known tornadoes
  6. 6. SCALE WIND SPEED POSSIBLE DAMAGE Enhanced, Operational Fujita Scale F0  40-72 mph Light damage: Branches broken off trees; minor roof damage EFO 65-85 mph F1 73-112 mph Moderate damage: Trees snapped; mobile home pushed off foundations; roofs damaged EF1 86-110 mph F2 113-157 mph Considerable damage: Mobile homes demolished; trees uprooted; strong built homes unroofed EF2 111-135 mph F3 158-206 mph Severe damage: Trains overturned; cars lifted off the ground; strong built homes have outside walls blown away EF3 136-165 mph F4 207-260 mph Devastating damage: Houses leveled leaving piles of debris; cars thrown 300 yards or more in the air EF4 166-200 mph F5 261-318 mph Incredible damage: Strongly built homes completely blown away; automobile-sized missiles generated EF5 over 200 mph
  7. 7.  Attempts to warn of tornadoes began in the United States in the mid-20th century.  Before the 1950s, the only method of detecting a tornado was by someone seeing it on the ground. Often, news of a tornado would reach a local weather office after the storm.  Today, we use weather radar to detect tornadoes.  In the United States and a few other countries, Doppler weather radar stations are used. These devices measure the velocity and radial direction of the winds in a storm, and so can spot evidence of rotation in storms from more than a hundred miles (160 km) away.
  8. 8.  http://www.youtube.com/watch?v=nlwnfXTx4F8

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