Cloud Formation

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• Science
• 7th Grade

Cloud Formation

How do clouds form?

Are all clouds the same?

What are nuclei?

Condensation

Have you ever had a cold cup of water and over time, the outside of the cup becomes wet? This is a process called condensation.

The warm moisture in the air touches the cold cup and cools to the dew point and condenses to liquid.

Nuclei

Nuclei are small particles that are found in the atmosphere that can either be solid or liquid.

Water molecules will condense onto the nuclei creating cloud droplets.

Graphic from: National Weather Service. (2025, July 1). How clouds form. National Oceanic and Atmospheric Administration. https://www.weather.gov/jetstream/clouds

Which of these cannot be used as cloud condensation nuclei?

A

Sea salt particles

B

Volcanic ash

C

Pure water vapor

D

Pollen grains

Dewpoint

Air is only able to hold a limited amount of moisture.

The measurement for how much moisture is in the air is called the dewpoint. When the dewpoint is the same as the air temperature, the air is fully saturated, and condensation happens.

This most commonly happens from the air rising.

Rising air.

A block of air, known as a parcel, will rise into the atmosphere, as this happens the parcel expands which results in cooling.

This process of a parcel expanding or contracting,

resulting in temperature changes, is known as the

adiabatic process.

For every 1,000 feet a parcel rises, it's air temperature

will decrease by 5.5℉ until it reaches saturation and

condenses. This process is called the "dry lapse rate."

National Weather Service. (2025, July 1). How clouds form. National Oceanic and Atmospheric Administration.

https://www.weather.gov/jetstream/clouds

Why do clouds change shapes?

The atmosphere is a volatile environment.

As air parcels rise, dry air may get mixed in, causing evaporation.

Condensation and evaporation are constantly happening, and when there is more condensation than evaporation, clouds grow. Conversely, clouds will dissipate when there is more evaporation than condensation.

Which of these is a real cloud name?

A

Cloudmist

B

Airpuff

C

Horizonveil

D

Altostratus

Types of clouds

Cumulus

Cumulus clouds are typically defined by their puffy look. Cumulus clouds usually also have a flat base to them.

These are considered vertical development clouds. They start developing lower in the atmosphere and then increase in height.

Nimbus

Nimbus clouds are rain producing clouds. They are distinct for their thick and dark look, which leads to gloomy weather.

Nimbus clouds come in two main types, nimbostratus which are low-level clouds responsible for consistent rain, as well as cumulonimbus.

Cumulonimbus

Cumulonimbus clouds are known for producing thunderstorms.

These clouds are distinct for their towering shape. These clouds often produce an anvil top where the condensation reaches a layer stable air(When the temperature no longer decreases with height) in the tropopause. Since the air cannot rise further, it spreads out.

Nimbostratus

Cumulonimbus

Stratus

Stratus are low-level clouds characterized by their distinctive flat nature.

Think back on a cloudy day, Stratus clouds are most likely responsible for that day.

These clouds may also produce a drizzle.

Cirrus

Cirrus are high-level clouds.

They are characterized by their thin wispy look.

Cirrus clouds receive this look from being formed from condensing ice particles as opposed to liquid water, due to their elevation putting them in ambient air temperature well below freezing.

Cloud Classification by Altitude

Mid-level

Cirrus
Cirrostratus

Cirrocumulus

High-level

Altostratus

Altocumulus

Low-level

Stratus

Stratocumulus

Nimbostratus

Vertical development

Cumulus

Cumulonimbus

What are some benefits of clouds?

Clouds are a key ingredient in regulating the temperature of the Earth.

Some clouds reflect solar energy back into space, keeping us cool. Other clouds act like a blanket, trapping heat keeping us warm.

As clouds become storms, these

storms can transfer energy from

the equator to the poles allowing

for the sun's energy to be spread

evenly across the Earth's surface.

National Aeronautics and Space Administration. (2005). The importance of understanding clouds (FS-2005-9-073-GSFC). NASA Earth-Sun System Division. https://earthobservatory.nasa.gov