Tornados

\ General Info

  • Generated in regions of already severe thunderstorms 
  • Two prime factors for tornado initiation    * The general topography    * The local climate 
  • Created over areas where air is undisturbed by mountains    * Very common in midwest US    * Known as tornado alley (tx, ok, ks, nb, ia, mo, il)   * Most rare in alaska, texas has the most    * Average by area though is florida 
  • Is tornado alley changing with the changing climate    * Gradually shifting eastward

Tornado Formation  

  • Average dimensions    * Width: 75 yrds    * Track length: 1-4 miles (how long its on the ground)   * Time on ground: 5 minutes    * Forward speed: 25 mph
  • Timing    * Prime season for the combination of ideal conditions      * Spring to early summer      * Although this appears to be shifting earlier    * Prime time of day     * Late afternoon to late evening        * Time of maximum local ground and atmosphseric heating        * The hottest part of the day
  • Tornado structure   * Combinations of opposing wind patterns    * High level, relatively dry/cooler winds from the west    * Lower level, warm/wet winds from the southeast originating in the golf of mexico 
  • Windows from cyclonic rotation parallel to the ground (called rollers)   * Large thunderstorms pull warmer air upward from low levels    * warm/wet air provides energy for the storm
  • Formation    * Large updrafts can cause a roller to tip into a vertical position      * Tornado is born upon touchdown with the ground   * Large storms can produce more than one tornado     * Called tornado families or storms      * Ex - large tornado swarm in 1974 caused damage to 13 states from AL to OH       * 148 tornados touched down in about 16 hours        * 307 killed    * Severe pressure drops (measured on a barometer)      * Inside a twister can be as low as 3” mercury      * For comparison        * Average daily pressure her is 31-32”   * Movement      * Track direction is generally SW to NE      * Combination of the prevailing wind direction from the west      * The CCW rotation of the tornado
  • Fujita scale   * Varies from EF0 to EF5      * EF0 - weakest, with winds of 65-85 mph and minor damage to building/trees     * EF5 - strongest with winds of >200 mph and complete destruction    * Precise wind speed numbers are actually estimates based on damage after the storm and not measured directly during    * EF0 = light damage some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged   * EF1 = Moderate damage. Peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off roads   * EF2 = Considerable damage. Roofs torn off frame houses; mobile homes demolished; train cars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground   * EF3 = Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown.   * EF4 = Devastating damage. Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated.   *  EF5 = Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 meters (109 yds.); trees debarked

Monitoring 

  • Early 1980s    * Device called TOTO   * Designed to get swept up into a tornado and measure all the atmospheric parameters of a tornado from the inside   * Scientists had to race to get ahead of a tornado and place the 400 pound cylinder squarely in its path   * Never actually worked
  • Storm prediction center    * Located in norman OK   * Monitors regional weather conditions every morning    * Issues a risk warning for severe weather later that day    * Interacts with national weather service 
  • National severe storms lab   * Use of doppler radar      * Measures the frequency change of objects moving away from the antenna      * Interpets mesocyclones 
  • Mobile doppler radar   * Operated on a mobile platform to image nearby tornadic activity    * Can get much closer to the tornado to image it more clearly 

Mitigation 

  • No practical efforts    * Most injuries/death occur from flying objects or being picked up and thrown around 
  • Scientific instrumentation and early warning systems are being improved    * Detection lead times are only a matter of minutes to no more than an house    * Very localized tracking by local tv 
  • Safe rooms lined with concrete 

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