Thunderstorms begin when strong updraughts build up towering cumulonimbus clouds.
Water drops and ice crystals in thunderclouds are buffeted together. They become charged with static electricity.
Negative charges sink to the base of a cloud; positive ones rise. When the different charges meet they create lightning.
Sheet lightning is a flash within a cloud. Forked lightning flashes from a cloud to the ground.
Forked lightning begins with a fast, dim flash from a cloud to the ground, called the leader stroke. It prepares the air for a huge, slower return stroke a split second later.
Thunder is the sound of the shock wave as air expands when heated instantly to 25,000°C by the lightning.
Sound travels more slowly than light, so we hear thunder three seconds later for every 1 km between us and the storm.
At any moment there are 2000 thunderstorms around the world, each generating the energy of a hydrogen bomb. Every second, 100 lightning bolts hit the ground.
A flash of lightning is brighter than 10 million 100-watt light bulbs. For a split second it has more power than all the power stations in the USA put together. Lightning travels at up to 100,000 km per second down a path that is the width of a finger but up to 14 km long. Sheet lightning can be 140 km long.
Lightning can fuse sand under the ground into hard strands called fulgurites.
Few places have more spectacular lightning displays than Nevada, USA. The energy in clouds piled up during hot afternoons is unleashed at night.