The mature stage is reached when down drafts develop and precipitation falls from the cloud. The cloud is then a full fledged thunderstorm and all hazards such as turbulence and lightning reach their greatest intensity. Raindrops that repeatedly ride strong vertical currents to the top of the cloud can end up as hailstones. Once a droplet has frozen, others attach themselves to it as it rises and falls in the cloud. It drops to the earth as a hailstone when it becomes too heavy for the updrafts to support.
Hailstones vary in size, depending upon the growth of the cloud where it originated.
The smallest hailstone is about the size of a pea. Lightning usually does not occur in a thunderstorm until its top spreads laterally into an ice crystal anvil-shaped cloud. The vigorous upward and downward motion of the currents and the friction created by the collision and jostling of various sized raindrops appears to be the mechanism that alters the normal electrical field of the atmosphere. The friction created by the movement of various sized rain drops and ice crystals results in the larger droplets being negatively charged while the smaller are positively charged. The location of electrical centers within a thunderstorm is determined by the weight and size of the droplets and the strength of the vertical currents.