ADN

With all the attention being given to natural disasters at the moment, I thought that I'd take the time to research and point out a few things about what is known as the most destructive card mother nature can play, the tornado...

What it is

By definition, a tornado is a violently rotating column of air extending from a thunderstorm to the ground... In an average year, about 1,000 tornadoes are reported across the United States, resulting in 80 deaths and over 1,500 injuries...The most violent tornadoes are capable of tremendous destruction with wind speeds of 250 mph or more...Damage paths can be in excess of one mile wide and 50 miles long...Tornadoes come in all shapes and sizes and can occur anywhere in the U.S. at any time of the year. In the southern states, peak tornado season is March through May, while peak months in the northern states are during the summer....


The Oldest Known Picture of a Tornado, taken August 28, 1884 near Howard, South Dakota.

What causes them

Thunderstorms develop in warm, moist air in advance of eastward-moving cold fronts. These thunderstorms often produce large hail, strong winds, and tornadoes. Tornadoes in the winter and early spring are often associated with strong, frontal systems that form in the Central States and move east. Occasionally, large outbreaks of tornadoes occur with this type of weather pattern. Several states may be affected by numerous severe thunderstorms and tornadoes.

During the spring in the Central Plains, thunderstorms frequently develop along a "dryline," which separates very warm, moist air to the east from hot, dry air to the west. Tornado-producing thunderstorms may form as the dryline moves east during the afternoon hours.

Along the front range of the Rocky Mountains, in the Texas panhandle, and in the southern High Plains, thunderstorms frequently form as air near the ground flows "upslope" toward higher terrain. If other favorable conditions exist, these thunderstorms can produce tornadoes.

Tornadoes occasionally accompany tropical storms and hurricanes that move over land. Tornadoes are most common to the right and ahead of the path of the storm center as it comes onshore.

How they form


Before thunderstorms develop, 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 within the thunderstorm updraft tilts the rotating air from horizontal to vertical...


An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.


A lower cloud base in the center of the photograph identifies an area of rotation known as a rotating wall cloud. This area is often nearly rain-free. Note rain in the background.


Moments later a strong tornado develops in this area. Softball-size hail and damaging "straight-line" winds also occurred with this storm.

Shapes and Sizes

• Shown: Weak // Strong // Violent Tornadoes
  
  Weak Tornadoes
  
  * 69% of all tornadoes
  * Less than 5% of tornado deaths
  * Lifetime 1-10+ minutes
  * Winds less than 110 mph
  
  Strong Tornadoes
  
  * 29% of all tornadoes
  * Nearly 30% of all tornado deaths
  * May last 20 minutes or longer
  * Winds 110-205 mph
  
  Violent Tornadoes
  
  * Only 2% of all tornadoes
  * 70% of all tornado deaths
  * Lifetime can exceed 1 hour
  * Winds greater than 205 mph
  • Tornado Myths
    
    MYTH: Areas near rivers, lakes, and mountains are safe from tornadoes.
    FACT: No place is safe from tornadoes. In the late 1980's, a tornado swept through Yellowstone National Park leaving a path of destruction up and down a 10,000 ft. mountain.
    
    MYTH: The low pressure with a tornado causes buildings to "explode" as the tornado passes overhead.
    FACT: Violent winds and debris slamming into buildings cause most structural damage.
    
    MYTH:Windows should be opened before a tornado approaches to equalize pressure and minimize damage.
    FACT: Opening windows allows damaging winds to enter the structure. Leave the windows alone; instead, immediately go to a safe place.
    
    Enviromental Clues
    
    Look out for:
    • * Dark, often greenish sky
      * Wall cloud
      * Large hail
      * Loud roar; similar to a freight train
      • Tornado Safety
        
        • # In a home or building, move to a pre-designated shelter, such as a basement.
          # If an underground shelter is not available, move to an interior room or hallway on the lowest floor and get under a sturdy piece of furniture.
          # Stay away from windows.
          # Get out of automobiles.
          # Do not try to outrun a tornado in your car; instead, leave it immediately.
          # Mobile homes, even if tied down, offer little protection from tornadoes and should be abandoned.
          • Fujita Tornado Damage Scale
            
            Many of us have heard the term F-3 and such, which is used to determine the strength and category of tornadoes..
            
            • Category F0: Light Damage (<73 mph); Some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged.
              
              Category F1: Moderate Damage (73-112 mph); Peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off road.
              
              Category F2: Considerable Damage (113-157 mph); Roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.
              
              Category F3: Severe Damage (158- 206 mph); Roofs and some walls torn off well-constructed houses, trains overturned; most trees in forest uprooted; heavy cars lifted off ground and thrown.
              
              Category F4: Devastating Damage (207- 260 mph); Well-constructed houses leveled; structure with weak foundations blown off some distance; cars thrown and large missiles generated.
              
              Category F5: Incredible Damage (261- 318 mph); Strong frame houses lifted off foundations and swept away; automobile sized missiles fly through the air in excess of 100 meters (109 yards); trees debarked; incredible phenomena will occur.
              • Tornado Fast Facts
                
                * Tornadoes are transparent until they pick up dust and debris...
                
                * A tornado that forms over water is called a "waterspout"...
                
                The Deadliest, Biggest and Costliest Outbreaks
                
                * The Tri-State Tornado Outbreak of March 18, 1925 killed 689 people in Missouri, Illinois and Indiana. Murphrysboro, Ill., had 234 of those deaths and West Frankfort, Ill., had 127;
                
                * Other deadly tornadoes include the May 6, 1840 tornado that killed 317 people in Natchez, Miss.; and the May 27, 1896, tornado killed 255 in St. Louis, Mo. In 1936, tornadoes on successive days killed 216 people in Tupelo, Miss., on April 5, and 203 people in Gainesville, Fla., on April 6;
                
                * The April 3 - 4, 1974 Super Outbreak was the largest known outbreak, with 148 tornadoes in 11 states, killing 315 people, injuring more than 5,300 and causing damage in excess of $600 million. Alabama, Kentucky and Ohio were the states hardest hit. Perhaps the most notable tornado of the outbreak was the one that began southwest of Xenia, Ohio. The violent tornado killed 34 people and destroyed half the town. Damages were more than $100 million;
                
                * The second most devastating outbreak of tornadoes in modern record was the 1965 Palm Sunday outbreak. Severe thunderstorms in the Upper Midwest spawned a total of 48 tornadoes within 12 hours. Indiana, Ohio and Michigan were hardest hit. These tornadoes killed 256 people and caused more than $200 million in damages. Two powerful tornadoes, about 30 minutes apart, traveled almost identical paths across Branch, Hilsdale, Lenawee and Monroe counties in extreme south-central and southeastern Lower Michigan, and killed 44 people. In Lenawee County the damage path was four miles wide. Damage caused by these two tornadoes was more than $32 million dollars.
                
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                ** This article was taken in whole or in part from sources located on the http://www.noaa.gov/ homepage... **