Lightning is a discharge of a large electrostatic charge that builds up on clouds near the surface of the earth during atmospheric disturbances such a thunderstorms.

In the atmospheric electrical discharge, a leader of a bolt of lightning can travel at speeds of 60,000 m/s (130,000 mph), and can reach temperatures approaching 30,000 °C (54,000 °F), hot enough to fuse silica sand into glass channels known as fulgurites which are normally hollow and can extend some distance into the ground. There are some 16 million lightning storms in the world every year.

Lightning can initially be formed by condensed water in clouds freezing into hail, then being blown by wind. The wind smashes the hail together, separating positive and negative charges. When enough negative charges build up, lightning is formed and strikes the tallest object near it.

Lightning discharges can be classified into two types:

1. Cloud to ground (CG) discharges. These discharges have at least one channel connecting the cloud to the ground [CG; or cloud to water (CW)].

2. Cloud discharges that have NO channel to ground. These cloud discharges are, in turn, classified as in-cloud (IC), cloud to air (CA), and cloud to cloud (CC).

A “CG” lightning discharge is typically initiated inside the thundercloud. It is first apparent when a faint negatively charged channel, the stepped leader, emerges from the base of the cloud. Under the influences of the electric field established between the cloud and the ground, the leader propagates towards the ground in a series of luminous steps of about 1 microsecond in duration and 50 to 100 meters in length, with a pause between steps of about 50 microseconds. The stepped leader reaches the ground in tens of milliseconds depending on the tortuosity of its path.

How lightning initially forms is still a matter of debate. Scientists have studied root causes ranging from atmospheric perturbations (wind, humidity, friction, and atmospheric pressure) to the impact of solar wind and accumulation of charged solar particles.

Ice inside a cloud is thought to be a key element in lightning development, and may cause a forcible separation of positive and negative charges within the cloud, thus assisting in the formation of lightning.

DURING A LIGHTNING STORM, seek shelter in a house or large building. Stay away from windows and metal objects, such as radiators.