Tornado
Breeding Ground
The United States is the world's tornado capital. Although tornadoes occur throughout the world, including India and Bangladesh, they are most intense and devastating in the United States--especially in Tornado Alley.
On average the United States experiences 100,000 thunderstorms each year, causing more than 1,000 tornadoes. (1990-1995) The National Weather Service says an average of 42 people are killed by tornadoes each year. (1986-1995) If you're interested, check out the complete statistics here.
Tornadoes are so common in Tornado Alley because of mountains to the west and the Gulf of Mexico to the south, explains meteorology professor Howard Bluestein. Bluestein teaches at the University of Oklahoma and is a veteran storm chaser.
"Supercells [large, powerful thunderstorms] that spawn tornadoes require strong vertical wind shear [changes in wind speed and direction with height] and lots of instability," he says. And that's exactly what happens in Tornado Alley.
In spring, Bluestein says, a strong westerly jet stream flows across the Alley. This upper air pattern creates instability and a trough of low pressure, drawing in warm, moist air from the Gulf.
Tornadoes can strike at any time of day, but they are much more frequent in the afternoon and evening, after the heat of the day has produced the hot air that is a requirement of a tornadic thunderstorm (defined).
How Fast is a Fast Twister?
|
|
  |
 |
There are 1 2
3 4
5 6 7
8 9 10
11 12 13
14 documents. (Glossary
| Bibliography)
Home
Page
This
lesson created by "The Why
Files," a NISE project funded by the NSF. Lesson used by permission.
Original lesson and graphics copyright NISE. Modifications copyright BPNM.