Thunderstorms result from rapid upward movement of warm, moist air, which form very high (even more than 20 km) cumulonimbus clouds. They are common in tropical regions during the rainy season, but can occur around the globe depending on the season of the respective regions. If you see a towering cauliflower-like cloud with its upper part anvil-like, it is an imminent sign of a thunderstorm brewing or in progress. From nearby, the shape is masked, often the sky just is dark (while the cloud at a distance often is bright white – depending on what side you see).

Lightning tends to hit the highest object towering from the ground, so avoid hill tops and open areas and do not seek shelter under a high or lone tree. Get indoors if possible or crouch down on the ground if there's no shelter. Cars with enough steel (many modern ones are mostly plastic) form Faraday cages and are thus safe, but avoid driving if possible. Avoid anything connected to power lines, phone lines etc., as electricity induced by a lightning strike can travel far along these. Swimming or taking a shower is dangerous for the same reason.

When a storm is approaching, unplug your electronic devices to avoid risk of having them fried by a lightning-induced power surge. If you plan to spend a lot of time in a high-risk area, get a surge protector. These are reasonably cheap devices that go between your computer or other valuable device and the wall socket; they do not give perfect protection, but they do greatly reduce risk.

In a semi-open area the safest position is at a distance about half the height from a tree or other high object – if the lightning strikes here, it will hit that object instead of you; the strong sound, electricity spread in the ground and pieces flying from the hit object are still dangerous. Parts of the lightning can even bounce off to people in the vicinity. Keep your feet together so that electricity in the ground does not travel between them through you. Spread out, so that if somebody gets hurt, the others are unharmed and ready to help.

Thunderstorms can be seen anywhere in the world except polar regions of northern Canada and the equivalent elsewhere. They can develop anywhere at anytime in the world but the most common times are afternoons and evenings. They are most common in the USA particularly east of the Rocky mountains. Western states get storms too but nowhere as intense and frequent. Supercells, extremely powerful thunderstorms with hail and tornadoes are most often seen in the Great Plains, the Midwest and the Southern states. Areas outside the States for supercells include southern Canada, continental Europe and Australia. Always listen to thunderstorm warnings and never ignore them.

Hail is the falling of solid balls of ice during a thunderstorm. Hailstorms are not very common but are a risk in some areas such as the Canadian Prairies and some regions of Australia. In mid-latitudes and tropical regions, they typically occur in spring or transition from wet to dry season.

In most storms, the hailstones are about the size of a pea; being bombarded with these can be quite unpleasant but is not really dangerous. Some storms have larger stones, golf ball-size or more, and these are definitely dangerous; they can shatter a car's windshield or knock a person unconscious!

If there is a threat of hail, bring all people, pets, and your car to an indoor space (your house or a garage) to avoid harm and hurt, and get away from windows or openings when hail hits.

Main article: Tornado safety

In a few parts of the world, especially in the United States, thunderstorms can also spawn tornadoes, spinning columns of air that suck everything they blow inward and upward. They can have winds up to hurricane-force speeds (more than 100mph/160kph) and travel along a swath of area. They typically last up to an hour at most, but often come with little warning especially for those unaware. They have been known to down trees and power lines, and even hoist a house from its foundation!

Tornadoes typically occur in spring especially in mid-latitude countries. Large and organized weather systems that span across multiple states can spawn a tornado outbreak; which are multiple tornadoes forming within a wide area.

Spotting a tornado is easy at daytime but dangerously difficult at night. If you see a funnel coming down from a dark cloud or debris & dirt flying high, it is a good sign that a tornado is about to happen at that very spot. Hail, especially of larger size, usually precedes a brewing tornado. If you can't spot any of them at night, watch the weather forecast on TV or listen on the radio. In some localities, sirens warn of an incoming tornado in the immediate area from which you must seek shelter immediately. Fleeing a tornado by motorcar can be tough because heavy rains may blind drivers from seeing a tornado and its direction of travel.

Tornadoes can occur anywhere in the world under the right conditions except polar regions. They are most common in the US with the Great Plains, the Midwest and Southern states being the highest risk. Other regions get them too but not as intense and frequent usually. Southern Canada ranks 2nd for highest number of tornadoes per year with the high risk areas including southern Manitoba, Saskatchewan and Alberta.

• Cyclones
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