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Weather and climate


A very powerful storm in Ontario, CanadaA very powerful storm in Ontario, CanadaClick to play video There are many different kinds of storm. Most involve severe, violent weather with regions of high winds and heavy rain, and perhaps a sudden change in temperature. Some have thunder and lightning. They move across sea and land and may cause great damage and loss of life. Powerful winds in tornadoes or hurricanes blow down buildings and bridges and toss cars and trucks about like toys. Heavy rain or snow causes floods, mudslides or avalanches.

Forked lightning during a thunderstormForked lightning during a thunderstorm

How storms occur

Most storms begin as the Sun heats an area of land or sea and causes warm air to rise rapidly. Storms vary greatly in size and duration. A small tornado or “twister” may have a base just a few metres across and be gone in half an hour. A typical thunderstorm is 5–10 kilometres (3–6 miles) wide and lasts for a few hours. A large hurricane may be more than 2000 kilometres (about 1250 miles) across and rage on for two or three weeks.

The sudden increase in temperature from lightning—to about 30,000°C (54,000°F)—produces a rapid expansion of the air, causing a shock wave: the sound of thunder.

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