It can be seen as the rain that falls from clouds and it also includes snowfall, hail, sleet, freezing rain, and even drizzle.
Understanding precipitation provides an insight into how our world works – and we have all you need to know and to understand more!
What Is Precipitation?
Precipitation refers to water droplets or ice crystals in the air that fall down to Earth.
Raindrops are formed when warm moist air rises up through the atmosphere and cools as it moves higher.
As the air cools, moisture condenses out of the air and forms tiny drops of liquid water. These small droplets then fall back to Earth as rain.
The word “precipitate” comes from the Latin word ”praecipitare” meaning “to throw down”.
This is because the falling drops of water look like they’re being thrown down by the wind. There are a number of different types of precipitation, and these include:
Rain
Rain is a form of precipitation that we are all familiar with, and it’s one of the most common types of precipitation.
When it rains, the sky becomes cloudy and the sun disappears behind the clouds. You may see thunderstorms during heavy rainfall, but this isn’t always the case.
Sometimes, there will be no storms at all.
Snow
Snow is another type of precipitation that is very different from rain. Snowflakes are made up of frozen water particles called ice crystals.
Ice crystals are formed when cold air meets warm air. Water molecules in the warmer air become attached to each other and form long chains of ice.
These chains of ice eventually grow so large that they break apart and turn into individual water droplets.
Hail
Hail is a type of precipitation that looks similar to snow. However, hail is actually composed of solid pieces of ice rather than snowflakes.
Hail occurs when a cloud has been disturbed by strong winds. As the cloud passes over the surface of the Earth, the wind causes the cloud to rotate around its center.
This rotation creates vortices within the cloud, which cause the cloud to spin rapidly.
As the spinning continues, the cloud begins to rotate faster and faster until it breaks apart and releases hailstones.
Freezing Rain
Freezing rain is a type of precipitation where rain freezes in contact with the ground.
Freezing rain usually happens when temperatures drop below 32 degrees Fahrenheit (0 degrees Celsius).
If the temperature is colder than 32 degrees F (-0 degrees C), then the rain will freeze before it reaches the ground.
Drizzle
Drizzle is a light misty rain that doesn’t last for long. It often appears after a storm has passed.
It’s not uncommon for drizzles to occur in areas that don’t normally experience much rain.
Fog
Fog is a low-lying layer of foggy air that covers land and sea. Fog is created when warm moist air rises above cooler air.
The rising warm air cools as it travels upwards, causing the water vapor in the air to condense.
Fog can sometimes appear in places that aren’t typically associated with fog.
For example, you might find fog forming in an area that has never experienced any fog before.
Precipitation Patterns
There are three main types of precipitation patterns: Cumulonimbus, Stratiform, and Stratus.
Cumulonimbus
A cumulonimbus cloud is a type of cloud that has a rounded top and bottom. Cumulonimbus clouds are usually found at mid-latitude regions during the winter months.
They are formed when a storm produces a large amount of rain. Raindrops fall through the cloud and collect on the underside of the cloud.
This collection of water drops causes the cloud to grow larger. Eventually, the cloud reaches its maximum size and begins to lose mass.
At this point, the cloud becomes unstable and breaks apart. The broken pieces of the cloud fall back to the ground as snowflakes.
Stratiform
A stratiform cloud is similar to a stratus cloud except that it does not have a rounded shape. Instead, it looks flat and smooth.
Stratiform clouds are typically seen in summertime. They are formed when hot air rises above cooler air.
When the hot air meets the colder air, condensation occurs. Condensation is the process by which water vapor changes into liquid water.
Stratus
A stratus cloud is a thin layer of cloud that covers most of the sky. It is usually associated with fair weather.
Stratus clouds are made up of tiny droplets of water suspended within the air. As the air moves over the Earth, the droplets move along with it.
The movement of the droplets causes them to collide with each other. This collision causes the droplets to become bigger.
Eventually, the droplets reach their maximum size and begin to break apart. The broken pieces fall down to the surface as rain.
The formation of precipitation depends on many factors including temperature, humidity, barometric pressure, and wind speed.
Temperature
Temperature directly impacts the formation of precipitation by affecting the rate at which moisture evaporates from the Earth’s surface.
Higher temperatures increase evaporation rates. Therefore, higher temperatures result in more precipitation. When air warms up, it expands.
As the air expands, it takes up more space and pushes aside surrounding air. This causes the surrounding air to move away from the warming air.
Air that is moving away from the heating source is said to be “warmer” than the air that is being heated. When air warms up, heat energy is transferred to the air.
This means that the air is getting hotter. As the air gets hotter, it also becomes less dense.
Less dense air is lighter than denser air. Therefore, the less dense air rises higher than the denser air.
As the denser air moves upward, it leaves behind the less dense air. When this happens, the denser air sinks back down toward the surface of the Earth.
This sinking motion is known as convection. Convection is responsible for most of the movement of clouds.
Convection
As mentioned, convection also plays a role in the formation of precipitation. Warm air near the surface of the Earth tends to rise.
This rising air is called a thermal plume. A thermal plume is like a chimney that draws warmer air into itself. As the air rises, it cools off.
This cooling process causes the air to become less dense. Because the air is becoming less dense, it falls back toward the surface of the Earth.
This falling air is called a downdraft. Downdrafts are important because they help create the conditions necessary for precipitation.
The downdrafts bring cold air from high altitudes down to the surface of the Earth where it mixes with the warmer air.
The mixing of these two different air masses results in a change in pressure. This change in pressure causes the air to rise.
Rising air is very unstable and therefore prone to breaking apart and releasing moisture.
The combination of rising air and descending air creates a situation where there is a difference in density between the warm air and the cold air.
This difference in density causes the warm air to sink while the cold air rises. The result is a vertical circulation pattern called a thunderstorm cell.
Wind Shear
Another factor that contributes to precipitation is wind shear. Wind shear occurs when winds blow across a temperature gradient.
In other words, if the wind blows over a large temperature range, then it will cause turbulence. Turbulence is the rapid swirling of air around objects.
It is often accompanied by strong updrafts or downdrafts. These updrafts and downdrafts can lead to severe weather such as tornadoes.
Tornadoes go hand in hand with precipitation, as they form in areas where there is a lot of instability in the atmosphere.
Tornadoes occur when an area of low pressure forms over a region of high pressure.
If the low-pressure system is not strong enough to overcome the high-pressure system, then the low-pressure system will collapse.
Collapsing low-pressure systems produce tornadoes.
Humidity
As the temperature increases, so does the rate of evaporation. However, the rate of evapotranspiration decreases as the temperature increases.
Evapotranspiration refers to the loss of water from plants due to transpiration (the transfer of water from plant roots to leaves).
Because evapotranspiration is less than evaporation, the total amount of water lost from the Earth’s surface also decreases.
This decrease in evapotranspiration results in lower levels of humidity. Lower levels of humidity lead to fewer clouds and therefore fewer precipitation events.
Barometric Pressure
As the atmospheric pressure decreases, the atmosphere can no longer hold as much water vapor.
This leads to an increase in the amount of water vapor in the atmosphere. Water vapor is what makes up clouds.
As the amount of water vapor increases, there will be more clouds. These clouds will eventually form precipitation.
Wind Speed
When winds blow across a body of water, they cause waves. Waves are created when water vibrates against another object.
If the wind blows faster than the waves, then the waves will travel away from the shoreline.
In contrast, if the wind blows slower than the waves, then they will travel toward the shoreline.
The direction of the wind determines whether or not the waves will travel toward or away from the shoreline and ultimately determine where the waves will deposit their energy.
If the wind blows too fast, then the waves will dissipate before reaching the shoreline. This means that the energy of the waves will not be transferred to the landmass.
On the other hand, if the wind blows too slowly, then the waves will continue moving toward the shoreline until they hit something solid.
At this point, the wave energy will be absorbed by the ground.
Turbulence And Air Stability
Precipitation is formed when the energy of the waves hits the ground. When the energy of the waves reaches the ground, it transfers its energy into the soil.
The soil becomes warmer because of the energy deposited into it. This warm soil creates convection currents, which we discussed earlier.
Convection currents are caused by hot air rising and cold air sinking. Hot air rises because it has less density than the surrounding air.
Cold air sinks because it has greater density than the surrounding air, thus causing the air to sink. Rising and sinking air causes the air to move around the Earth.
This movement of air causes the air to become unstable. Unstable air is characterized by having a large vertical component.
An example of unstable air would be a tornado. Unstable air is very turbulent, which is why it is called “turbulent”.
Turbulence is the rapid motion of air particles. It occurs when air moves rapidly over objects such as mountains, trees, buildings, etc.
Turbulence is caused by the interaction between two different types of air: stable air and unstable air. Stable air is calm and still.
It is composed of molecules that have low kinetic energy. Kinetic energy is the energy associated with movement.
Molecules that have high kinetic energy are said to be unstable. Instability is caused by the interaction of these two types of air.
Turbulence And Precipitation
So what does this have to do with precipitation? Well, when the energy of the unstable air interacts with the stable air, it causes turbulence.
This turbulence causes the air to rise and fall quickly. Because the air is rising and falling so quickly, it causes the air to cool and heat the surface of the Earth.
This cooling and heating of the surface of the Earth causes the temperature of the air to change.
This change in temperature causes the air to begin to rise again. Thus, an upward flow of air begins to form. When the air rises, it carries moisture with it.
As the air rises, it pulls moisture out of the atmosphere and deposits it on the surface of the Earth at higher elevations.
When the air falls back down, it brings moisture with it.
This process continues until all of the moisture in the air is deposited onto the surface of the Earth, forming precipitation.
Final Thoughts
Precipitation is an essential element of our planet and something that has a direct impact on our lives every single day.
Having a good understanding of just what it is and how it works allows us to better understand the world around us. Check out this excellent clip to learn more about precipitation and the types of precipitation.
Hi, my name is Andrew Capper and I have been a meteorologist for almost 30 years now. My line of work specializes in the scientific principles used to explain and understand the earth’s atmosphere and how that affects everyday life.
I created this website to share my knowledge and help others stay safe during extreme weather events.
I’ll be looking at weather forecasting, clouds, tornadoes, hurricanes, and much more - so, if you’ve ever been fascinated by the weather like I have been since I was a young boy, this is the site for you. Enjoy!
