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Forked lightning lights up the sky 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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