Shawnee, Oklahoma and Moore Oklahoma
What is a tornado?
A tornado is a mobile, destructive vortex of violently rotating winds having the appearance of a funnel-shaped cloud and advancing.
How dose a tornado form?
1. 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.
2. The first step causes rising air within the thunderstorm updraft tilts the rotating air from horizontal to vertical.
3. 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.
4. A lower cloud base in the centre of the photograph identifies an area of rotation known as a rotating wall cloud.
5.Moments later a strong tornado develops in this area. Softball-size hail and damaging "straight-line" winds also occurred with this storm.
Tornadoes usually result from a very large thunderstorm. Cold air and warm air combine, and the cold air goes down as the warm air rises. This warm air eventually twists into a spiral, forming a funnel cloud. As the sky turns a very dark green colour, the tornado begins its path of destruction.
The scale that is used to to measure tornadoes