Crystallization
The process of a substance going directly from a vapor form (water vapor) to a solid (ice) at the same temperature, without going through the liquid phase (water). The opposite of sublimation.
Water Vapor (H2O)
Water in gaseous form. It is one of the most import constituents of the atmosphere. Due to its molecular content, air containing water vapor is lighter than dry air. This contributes to the reason why moist air has a tendency to rise.
Ice
The solid form of water. It can be found in the atmosphere in the form of ice crystals, snow, ice pellets, and hail for example.
Temperature
The measure of molecular motion or the degree of heat of a substance. It is measured on an arbitrary scale from absolute zero, where the molecules theoretically stop moving. It is also the degree of hotness or coldness. In surface observations, it refers primarily to the free air or ambient temperature close to the surface of the earth.
Water
Refers to the chemical compound, H2O, as well as its liquid form. At atmospheric temperatures and pressures, it can exist in all three phases: solid (ice), liquid (water), and gaseous (water vapor). It is a vital, life-sustaining part of life on earth.
Sublimation
The process of a solid (ice) changing directly into a gas (water vapor), or water vapor changing directly into ice, at the same temperature, without ever going through the liquid state (water). The opposite of crystallization.