Formation, characteristics, and classification of tornadoes

Tornadoes: Nature's Phenomenon

What is a Tornado?

A tornado is "a violent, destructive, whirling wind accompanied by a funnel-shaped cloud that progresses in a narrow path over the land" (Merriam-Webster, Incorporated, 2012).

Tornadoes can develop in mere seconds and destroy everything in their path

Sometimes, a tornado will happen so quickly that there is little or no sign before it starts (Federal Emergency Management Association, 2012). A tornado can have the strongest winds on earth, up to 300 MPH, and can cause "fantastic destruction and great loss of life, mainly from flying debris and collapsing structures" (Snow, 2012).

How and What of Tornadoes

How, What

The National Severe Storms Laboratory studies tornadoes and says that tornadoes come from thunderstorms. Before the thunderstorm, the wind changes direction, becomes faster and becomes higher. Then it becomes an invisible spinning wind going horizontally in the lower atmosphere. While the thunderstorm is happening, air rises inside it and tilts the spinning air sideways so it is spins vertically. Then the spinning air becomes 2 -- 6 miles wide and stretches through a lot of the thunderstorm, and is where a tornado usually comes from. The area where the thunderstorm develops is usually free of rain although it is in a thunderstorm. Then in moments, a strong tornado can start and "touch down" on the ground (NSSL-NOAA, 1992).

C. Appearance

The Tornado Project says that that "you can get an infinite variety of possible tornado shapes" but the Project also talks about "skinny rope" tornadoes, wide and fat tornadoes, and water spouts, which are tornadoes over water (Tornado Project, 1999).

D. Rotation

Tornadoes start out rotating horizontally inside of thunderstorms, and then the "updraft" of air in the thunderstorm tilts the spinning air and makes it spin vertically (NSSL-NOAA, 1992). The vertically spinning air is usually what we see when we see a tornado. Tornadoes spin counter-clockwise in the Northern Hemisphere, except when there is a "rare anti-cyclonic tornado" that spins clockwise. In the Southern Hemisphere, tornadoes nearly always spin clockwise (Wiki Answers, 2012).

III. Different Levels of Tornadoes

A. Level System

Scientists use "the Enhanced Fujita Scale" to give tornadoes different levels. They started with the Fujita Scale and started using the Enhanced Scale in 2007 because it uses "three-second gusts estimated at the point of damage based on a judgment of 8 levels of damage to 28 indicators" (About.com, no date).

B. Least

The old scale had "F0" for the weakest level: the wind speed is 40-72 MPH and the damage is light, like tearing branches from trees, ripping out trees with shallow roots, damaging signs, traffic signals and chimneys (Brain & Lamb, 2012). The new scale has "EF0" for the weakest level.

C. Worst

The old scale had "F5" for the worst level: the wind speed is 261 -- 319 MPH and the damage is "incredible," with cars thrown through the air, houses destroyed and steel-reinforced concrete buildings seriously damaged (Brain & Lamb, 2012). The new scale has "EF5" as the worse level (About.com, no date).

IV. Seasonal Timing

A. When

The National Severe Storms Laboratory says that tornadoes happen all over the world and happen anywhere in the United States but that they usually happen in the U.S. "east of the Rocky Mountains during the spring and summer months" (NSSL-NOAA, 1992).

B. Where

The National Severe Storms Laboratory says tornadoes in the winter and early spring "form in the Central States and move east." The Laboratory also says that tornadoes are found in the Texas panhandle and in the southern High Plains (NSSL-NOAA, 1992). The Tornado Project says there are 3 "tornado alleys": from central Texas to Colorado, North Dakota and Minnesota; from Texas to Georgia; from Arkansas to the Ohio River and the Great Lake state of Ohio, Indiana, Illinois and Michigan (Tornado Project, 1999).