What is Precipitation and What are Different Types of Precipitation?


Precipitation is the falling of water from the sky in different forms. They all form from the clouds which are raised about 8 to 16 kilometers (4 to 11 miles) above the ground in the earth’s troposphere. Precipitation takes place whenever any or all forms of water particles fall from these high levels of the atmosphere and reach the earth’s surface. The drop to the ground is caused by frictional drag and gravity. When one falling particle drops from the cloud, it leaves behind a turbulent wake, causing faster and continued drops.

The (clouds) crystallized ice may reach the ground as ice pellets or snow or may melt and change into raindrops before reaching the surface of the earth depending on the atmospheric temperatures. For this reason, there are many different types of precipitation namely rain, snow, sleet, freezing rain, hail, snow grains, and diamond dust. They are forms of water that fall from the sky’s frozen clouds.

As per Wikipedia,

In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation include drizzle, rain, sleet, snow, graupel and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and “precipitates. Thus, fog and mist are not precipitation but suspensions, because the water vapor does not condense sufficiently to precipitate.

Different Types of Precipitation

1. Rain

Rain is any liquid that drops from the clouds in the sky. Rain is described as water droplets of 0.5 mm or larger. Droplets less than half a millimeter are defined as a drizzle. Raindrops frequently fall when small cloud particles strike and bind together, creating bigger drops. As this process continues, the drops get bigger and bigger to an extent where they become too heavy to suspend on the air. As a result, the gravity pulls then down to the earth.

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When high in the air, the raindrops start falling as ice crystals or snow but melt when as they proceed down the earth through the warmer air. Rainfall rates vary from time to time, for example, light rain ranges from rates of 0.01 to 0.1 inches per hour, moderate rain from 0.1 to .3 inches per hour, and heavy rain above 0.3 inches per hour. Rain is the most common component of the water cycle and replenishes most of the freshwater on the earth.

2. Snow

Snow occurs almost every time there is rain. However, snow often melts before it reaches the earth’s surface. It is precipitation in the form of virga or flakes of ice water falling from the clouds. Snow is normally seen together with high, thin, and weak cirrus clouds. Snow can at times fall when the atmospheric temperatures are above freezing, but it mostly occurs in sub-freezing air. When the temperatures are above freezing, the snowflakes can partially melt but because of relatively warm temperatures, the evaporation of the particles occurs almost immediately.

This evaporation leads to cooling just around the snowflake and makes it to reach to the ground as snow. Snow has a fluffy, white, and soft structure and its formation is in different shapes and ways, namely flat plates, and thin needles. Each type of snow forms under specific combinations of atmospheric humidity and temperatures. The process of snow precipitation is called snowfall.

3. Sleet (Ice Pellets)

Sleet takes place in freezing atmospheric conditions. Sleet, also known as ice pellets, form when snow falls into a warm layer then melts into the rain and then the rain droplets fall into a freezing layer of air that is cold enough to refreeze the raindrops into ice pellets. Hence, sleet is defined as a form of precipitation composed of small and semitransparent balls of ice. They should not be confused with hailstones as they are smaller in size.

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Sleet is often experienced during thunderstorms and is normally accompanied by frosty ice crystals that form white deposits and a mixture of semisolid rain and slushy snow. Ice pellets (sleet) bounce when they hit the ground or any other solid objects and fall with a hard striking sound. Sleet don does not freeze into a solid mass except when it combines with freezing rain.

4. Freezing Rain

Freezing rain happens when rain falls during below freezing conditions/temperatures. This normally results in the solidification of rain droplets. The raindrops are super-cooled while passing through the sub-freezing layer in the atmosphere and freezes by the time it reaches the ground. During freezing rains, it is common to witness an even coating of ice on cars, streets, trees, and power lines. The resulting coating of ice is called glaze and it can build up to a thickness of several centimeters. Freezing rains pose a huge threat to normal operations of roadway transportation, aircraft, and power lines.

5. Hail

Hailstones are big balls and irregular lumps of ice that fall from large thunderstorms. Hail is purely solid precipitation. As opposed to sleets that can form in any weather when there are thunderstorms, hailstones are predominately experienced in the winter or cold weather. Hailstones are mostly made up of water ice and measure between 0.2 inches (5 millimeters) and 6 inches (15 centimeters) in diameter. This ranges in size of a pea’s diameter to that larger than a grapefruit.

For this reason, they are highly damaging to crops, tearing leaves apart and reducing their value. Violent thunderstorms with very strong updrafts usually have the capability to hold ice against the gravitational pull, which brings about the hailstones when they eventually escape and fall to the ground. So, hailstones are formed from super-cooled droplets that slowly freeze and result in a sheet of clear ice.

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6. Drizzle

Drizzle is very light rain. It is stronger than mist but less than a shower. Mist is a thin fog with condensation near the ground. Fog is made up of ice crystals or cloud water droplets suspended in the air near or at the earth’s surface. Drizzle droplets are smaller than 0.5 millimeters (0.02 inches) in diameter. They arise from low stratocumulus clouds. They sometimes evaporate even before reaching the ground due to their minute size. Drizzle can be persistent is cold atmospheric temperatures.

7. Sun Shower

Sun shower is a precipitation event that is registered when rain falls while the sun shines. It occurs when the winds bearing rain together with rainstorms are blown several miles away, thus giving rise to raindrops into an area without clouds. Consequently, a sun shower is formed when a single rain cloud passes above the earth’s surface and the sun’s rays penetrate through the raindrops. Most of the time, it is accompanied by the appearance of a rainbow.

8. Snow Grains

Snow grains are very small white and opaque grains of ice. Snow grains are fairly flat and have a diameter generally less than 1mm. They are almost equivalent to the size of drizzle. Read more about snow grains here.

9. Diamond Dust

Diamond dust is extremely small ice crystals usually formed at low levels and at temperatures below -30 °C. Diamond dust got its name from the sparkling effect which is created when light reflects on the ice crystals in the air. You can read more about diamond dust here.

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