Rainfall

Hail

Another potentially destructive form of precipitation is rounded, lumpy grains of ice, called hail. Balls of hail, usually called hailstones, form during thunderstorms when ice crystals are tossed high inside thunderclouds by strong, turbulent air currents. Supercooled water droplets inside the clouds freeze onto these ice crystals and make each crystal larger by adding new icy layers. This type of growth pattern, called concentric layering, has a small center with layers surrounding it, much like the layering you find when you cut an onion in half. New layers continue to be added until the hailstones become too heavy for the air currents to carry, and the hailstones fall to the ground.
Hailstones range greatly in size. Pea- to marble-sized hailstones are common. During severe storms, air currents can be strong enough to support hailstones the size of golf balls, which can do great damage to plant life and property.

Several things can happen to precipitation when it reaches the earth's surface. Most precipitation lands on the ground or in surface water. About 15 to 20 percent of the rain that falls on land surfaces soaks into the ground. Some precipitation lands on plants, where it either remains on the leaves and eventually evaporates, or slides off and falls to the ground. More than half of the precipitation is returned to the atmosphere through evaporation and transpiration.
Water can be on the earth's surface and not be an active part of the hydrologic cycle. In or near polar regions or on mountaintops, temperatures are so cold that snow and ice can accumulate in deep layers and eventually form glaciers. Glaciers may last hundreds or even thousands of years. During this time, the frozen water is temporarily removed from the hydrologic cycle. Eventually, however, when the air temperature warms and melting occurs, snow and ice occupy the same place in the hydrologic cycle as rainwater.

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