Precipitation
Unlike evaporation and condensation, precipitation is not a process. Precipitation describes any liquid or solid water that falls to Earth as a result of condensation in the atmosphere. Precipitation includes rain, snow, and hail. Fog is not precipitation. The water in fog does not actually precipitate, or liquify and fall to Earth. Fog and mist are a part of the water cycle called suspensions: They are liquid water suspended in the atmosphere. Precipitation is one of many ways water is cycled from the atmosphere to the Earth or ocean.
After water vapor condenses forming ice crystals and water droplets, it can take on a variety of forms as it falls to the Earth as precipitation. Each of these forms of precipitation are unique with their own important characteristics. The main types of precipitation are rain, snow, sleet, freezing rain, and hail.
Rain
Rain is by far the most common type of precipitation in our atmosphere. Rain takes place when drops of liquid water fall all the way to the surface of the Earth. Rain often takes one of two main forms. These two forms are showers and drizzles. A shower lasts just a brief period of time, and usually is made up of large heavy drops. Drizzles generally last much longer, and are made up of smaller, finer droplets of water. Rain can either form as ice crystals melt or as a coalescence of many smaller water droplets.
Snow
Snow forms when water vapor turns directly into ice without ever passing through a liquid state. This happens as water condenses around an ice crystal. Snow can take the form of ice pellets or snow flakes. As snow falls to the ground, it often melts on the warm surface of the Earth. If the surface of the Earth is chilled sufficiently, snow begins to pile up, creating snow drifts. In some locations, such as mountains, these snow drifts can reach several feet or meters in depth.
Sleet
Sleet refers to a mixture of snow and rain as well as raindrops that freeze on their way down. Unlike snow, the raindrops pass through a liquid form before freezing. The result is that they are not light and fluffy.
Freezing Rain
Freezing rain, which is sometimes referred to as glaze, takes place when water droplets become super-chilled. They do not freeze in air, but rather freeze the instant they strike an object, such as a road or car. The result can make roads very slippery, and can cause car doors to become frozen shut.
Hail
Hail forms in a complex dance between moisture and wind. Deep within cumulonimbus clouds ice crystals form and begin to fall towards the Earth’s surface. As this happens, wind gusts pick up the ice crystals, pushing them back up high into the clouds. As they begin to again fall down, they continue growing in size. Again, a wind gust might catch the growing hail stones, pushing them back up high into the clouds. This process may be repeated several more times until the hail stones become so large that they are too heavy for the wind to carry, causing them to fall towards the Earth.
The amount of precipitation that a particular location receives is determined by a number of factors previously discussed in this chapter. These include the average temperature for an area, the maximum vapor limit, the humidity, the location of prominent land formations such as mountains, the proximity to oceans, the amount of wind, etc. The amount of precipitation that an area receives is referred to as that area’s average annual precipitation. A location with a relatively low average annual precipitation would be rather desolate. Little water means that there will be less life. These areas are often called deserts. Areas with high average annual precipitation are lush and bustling with life. These areas are often referred to as rain forests. Most of the Earth’s surface receives an average annual precipitation that lies somewhere between these two extremes.
After water vapor condenses forming ice crystals and water droplets, it can take on a variety of forms as it falls to the Earth as precipitation. Each of these forms of precipitation are unique with their own important characteristics. The main types of precipitation are rain, snow, sleet, freezing rain, and hail.
Rain
Rain is by far the most common type of precipitation in our atmosphere. Rain takes place when drops of liquid water fall all the way to the surface of the Earth. Rain often takes one of two main forms. These two forms are showers and drizzles. A shower lasts just a brief period of time, and usually is made up of large heavy drops. Drizzles generally last much longer, and are made up of smaller, finer droplets of water. Rain can either form as ice crystals melt or as a coalescence of many smaller water droplets.
Snow
Snow forms when water vapor turns directly into ice without ever passing through a liquid state. This happens as water condenses around an ice crystal. Snow can take the form of ice pellets or snow flakes. As snow falls to the ground, it often melts on the warm surface of the Earth. If the surface of the Earth is chilled sufficiently, snow begins to pile up, creating snow drifts. In some locations, such as mountains, these snow drifts can reach several feet or meters in depth.
Sleet
Sleet refers to a mixture of snow and rain as well as raindrops that freeze on their way down. Unlike snow, the raindrops pass through a liquid form before freezing. The result is that they are not light and fluffy.
Freezing Rain
Freezing rain, which is sometimes referred to as glaze, takes place when water droplets become super-chilled. They do not freeze in air, but rather freeze the instant they strike an object, such as a road or car. The result can make roads very slippery, and can cause car doors to become frozen shut.
Hail
Hail forms in a complex dance between moisture and wind. Deep within cumulonimbus clouds ice crystals form and begin to fall towards the Earth’s surface. As this happens, wind gusts pick up the ice crystals, pushing them back up high into the clouds. As they begin to again fall down, they continue growing in size. Again, a wind gust might catch the growing hail stones, pushing them back up high into the clouds. This process may be repeated several more times until the hail stones become so large that they are too heavy for the wind to carry, causing them to fall towards the Earth.
The amount of precipitation that a particular location receives is determined by a number of factors previously discussed in this chapter. These include the average temperature for an area, the maximum vapor limit, the humidity, the location of prominent land formations such as mountains, the proximity to oceans, the amount of wind, etc. The amount of precipitation that an area receives is referred to as that area’s average annual precipitation. A location with a relatively low average annual precipitation would be rather desolate. Little water means that there will be less life. These areas are often called deserts. Areas with high average annual precipitation are lush and bustling with life. These areas are often referred to as rain forests. Most of the Earth’s surface receives an average annual precipitation that lies somewhere between these two extremes.