1. Chapter 8

2.  A tornado is an extremely violent windstorm  It descends from the clouds for a few minutes to cause major destruction  Springtime is tornado season in the American interior

3.  Most tornadoes occur in the United States  An average of 655 tornadoes every year  Canada’s leading twister province, Ontario can expect only about 25 tornadoes a year  In both Canada and the United States, amateur storm trackers often exchange information about tornadoes using the iternet

4.  Tornadoes are rare events that are very difficult to track and predict  Tornadoes: ◦ touch down and lift off suddenly ◦ Sharply change direction ◦ Destroy a house and leave the next house untouched ◦ Winds of an F5 can twist heavy metal around a tree

5.  Prime time between mid-March and June  Usually strike between 3:00 – 6:00 pm  Fast rising currents of warm humid air star the process  Columns of cooler air rush down towards the ground to replace these rising currents  Descends from the sky

6.  Form a funnel of air known as the vertex  Winds can surpass 500 km/h  Travels across the ground at about 60 km/h  Winds inside the funnel rotate counter clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere

7.  Winds of a tornado are a major source of power and cause destruction in three ways ◦ Winds rotating around the vortex are powerful enough to blow down trees, tear off roofs and flatten buildings ◦ Pressure difference can cause building to implode (to cave in) due to the low pressure inside the funnel ◦ Air swirls upwards around the vortex and can lift very heavy objects  Strength of tornadoes is measured on the Fujita-Pearson scale.

8.  Technologies such as Doppler radar, aerial photography, and satellite imaging are used to track and report dangerous weather conditions  During a weather watch, a red band appears across the bottom of the television screen. It identifies the locations affected  If conditions worsen, a weather warning is issued, at which time the whole screen is coloured or flashes, and people in specific areas are advised to seek shelter