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Precipitation is any form of water, liquid or solid aqueous deposit, that fall from the clouds in the sky. It forms in the Earth's atmosphere and then drops onto Earth’s surface. Precipitation is an essential part of Earth’s water cycle because it connects the ocean, land, and atmosphere. [1] [2] [3] [4]

How it works

Droplets of water suspended in the air, also known as water vapor, build up in the Earth's atmosphere. From Earth, we see water vapor in the atmosphere as clouds and/or fog. Precipitation forms around the cloud condensation nuclei (CCN), or tiny pieces of material such as dust, that collects in clouds. Eventually, the clouds can’t hold the water vapor any longer and this creates precipitation in the form of a liquid or a solid.[1] Precipitation “can only fall to the Earth's surface if they grow to a size that can overcome updrafts." [3]

Where it comes from

“…most clouds do not produce precipitation. In many clouds, water droplets and ice crystals are just too small to overcome the natural updrafts found in the lower atmosphere. As a result, the tiny water droplets and ice crystals remain suspended in the atmosphere until they are converted back into vapor.” [3]

How it's measured

Certain kinds of precipitation, like rain and snow, has been measured for centuries using instruments as basic as containers with markings on them to very advanced, complex tools. Today, these specialized devices provide information about the size of raindrops to how wind impacts the measurements taken. Weather radar systems on the ground send out a pulse of energy into the clouds and that provides us with the information of where and how much precipitation there will be. Tools we use that aren’t stationed on the ground are the satellites orbiting above the Earth. These satellites give display a bigger picture of precipitation across the entire globe. [2]

Why it's measured

It is important to measure precipitation because each for affects every part of life on Earth in a different way. When we measure rain for example, we measure where it occurs and how much it occurs, so that scientists can get a better understanding of the impact of precipitation on streams, rivers, surface runoff and groundwater. “Frequent and detailed measurements help scientists make models of and determine changes in Earth’s water cycle” (NASA).

Kinds of Precipitation

The most common forms of precipitation are rain, snow, hail, and sleet.

Here's a picture of rain


Rain is the most commonly know form of precipitation that falls to Earth’s surface. Rain is known as small droplets of water that fall from the clouds when they get too big for the cloud to hold. As these drops fall, they grow larger in size as they collect more water on their way down. Most people picture raindrops the way cartoon pictures portray rain to look like tears, but real raindrops are spherical. “Raindrops must have a diameter greater than 0.5 millimeters and smaller than 5 millimeters. Raindrops that are any bigger in size are too heavy to be held together as a single drop.


Snow requires temperatures on the ground to be 32-degrees Fahrenheit or colder, and any snow that falls on a ground warmer than 32 degrees, melts on contact. Snow is precipitation that falls in the mid and high latitudes in the form of ice crystals. These ice crystals have a delicate, complex structure because they are formed individually in clouds. Snowflakes are so uniquely formed because ice crystals’ growth is the most rapid process. As the different patterned snowflakes fall to Earth’s surface, they cluster together depending on the temperature and humidity of the air. A “graupel” is when snow falls in the form of a ball instead of soft flakes, and this mostly happens “when snow is melted and precipitation forms around the snow crystal” (National Geographic). Snowfall tends to occur in the fall, winter, and spring months of the year because this is when atmospheric temperatures commonly drop below freezing. (Pidwirny).


Hail descends to earth from the clouds as small rock-like forms of hard, solid ice. Even though these pieces are typically small, they’ve been recorded as being as large as 6 inches wide. They’ve also been measured at weighing more than a pound, but this depends on the storm. The creation of hailstones starts in the highest part of each cloud during cold thunderstorms. The stones form through the upward movement of air through the clouds which freezes the water droplets and stops them from falling as water. Before the pieces fall to earth, the frozen droplets collect more cold water which makes the forms larger. Snowfall is usually calm, but hail storms are quite the opposite. (National Geographic). Eventually the hailstones become too heavy for the clouds and fall. Because of the stones’ heaviness, scientists have estimated that the stones have reached speeds of more than 80 mph on their descend. (NCAR).


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See also

Other closely related articles in this wiki include:


  1. 1.0 1.1 Society, N. G., & Society, N. G. (2011, February 15). precipitation. Retrieved March 22, 2016, from
  2. 2.0 2.1 Precipitation Measurement Missions | An international partnership to understand precipitation and its impact on humankind. (n.d.). Retrieved March 22, 2016, from
  3. 3.0 3.1 3.2 Pidwirny, M. (2011, September 10). Precipitation and fog. Retrieved March 22, 2016, from
  4. Precipitation. (n.d.). Retrieved March 22, 2016, from

External links

Relevant online sources to this wiki article include: