Chapter 8
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
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
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
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
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
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.
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