How Do Hail Stones Occur?

Hail stones form in strong thunderstorm clouds, particularly those with intense updrafts. These thunderstorms contain mainly supercooled water droplets, these are liquid droplets that have been cooled beyond their natural freezing point because of a lack of a seed crystal (or nucleus). When a seed crystal (condensation nuclei) is presented, such as bugs or dust, these water droplets freeze on contact. The ice nuclei that develop grow rapidly. If the hailstones grow large enough, latent heat released by further freezing may melt the outer shell of the hailstone, the wet growth that follows is more efficient because as well as the freezing of the supercooled droplets, the hailstone my also join together with other stones. Eventually, as the hailstone grows it becomes too heavy to be maintained by the clouds updraft and thus falls to the ground.
Hail storms are much more likely to occur in mountain ranges because the mountains force winds upwards intensifying the updraft.

It is a form of precipitation, where small lumps of snow falls onto Earth.