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