Lightning Science - Jasper Thompson Lightning Protection, Inc.

Air Movement
Updraughts and down-draughts of air are fairly common events experienced by most of us and, indeed, used by glider pilots and balloonists to further their flights or bring them to a premature end. Such movements of air may be generated

Thunder Cloud
A ‘thunder cloud’ is a cloud system of this type in which the air velocities are much greater than normal. The diagram below shows the wind, temperature and water (or ice) distribution in a thundercloud. The violent updraughts and downdraughts in the cloud centre generate static charges, the exact mechanism by which this occurs being still unknown. The observed result, however, is that the cloud accumulates positively charged ice crystals in the upper region and negatively charged water droplets in the lower region.
Point Discharges
In undisturbed fine weather, the earth carries a negative charge with the corresponding positive charge in the upper atmosphere. By convention, this results in a positive (downwards) field of typically 100V/m. Immediately below the thundercloud charge centre, the electric field may exceed 20kV/m. Fields of such magnitude can lead to point discharges taking place from sharp objects such as the tips of radio masts and flagpoles. These objects are essentially conductors short-circuiting part of the vertical field and hence producing an intense field concentration at the tip.

by heat coming from hillsides in full sun or by cold air masses pushing underneath warmer air in a frontal weather system. As the warm air rises, it progressively cools and forms a cloud consisting of water droplets and, at greater heights, ice crystals.